chore: update GitHub branch references to use HEAD

CONTRIBUTING.md

@@ -73,7 +73,7 @@ source ./sendgrid.env
 
 ##### Execute: #####
 
-See the [examples folder](https://github.com/sendgrid/php-http-client/tree/master/examples).
+See the [examples folder](examples).
 
 <a name="understanding-the-codebase"></a>
 ## Understanding the Code Base
@@ -88,11 +88,11 @@ Unit tests.
 
 **/lib/SendGrid/Client.php**
 
-An HTTP client with a fluent interface using method chaining and reflection. By returning self on [__call](https://github.com/sendgrid/php-http-client/blob/master/lib/client.php#L212) and [_()](https://github.com/sendgrid/php-http-client/blob/master/lib/client.pph#L198), we can dynamically build the URL using method chaining and [__call](https://github.com/sendgrid/php-http-client/blob/master/lib/client.php#L212) allows us to dynamically receive the method calls to achieve reflection.
+An HTTP client with a fluent interface using method chaining and reflection. By returning `$this` on [__call](lib/Client.php#L576), we can dynamically build the URL using method chaining and [__call](lib/Client.php#L576) allows us to dynamically receive the method calls to achieve reflection.
 
 This allows for the following mapping from a URL to a method chain:
 
-`/api_client/{api_key_id}/version` maps to `client->api_client().->_($api_key_id)->version-><method>()` where <method> is a [HTTP verb](https://github.com/sendgrid/php-http-client/blob/master/lib/client.php#L94).
+`/api_client/{api_key_id}/version` maps to `client->api_client().->_($api_key_id)->version-><method>()` where <method> is a [HTTP verb](lib/Client.php#L210).
 
 **/lib/SendGrid/Config.php**
 
@@ -103,9 +103,9 @@ Loads the environment variables.
 
 All PRs require passing tests before the PR will be reviewed.
 
-All test files are in the [`/test/unit`](https://github.com/sendgrid/php-http-client/tree/master/test/unit) directory.
+All test files are in the [`/test/unit`](test/unit) directory.
 
-For the purposes of contributing to this repo, please update the [`ClientTest.php`](https://github.com/sendgrid/php-http-client/blob/master/test/unit/ClientTest.php) file with unit tests as you modify the code.
+For the purposes of contributing to this repo, please update the [`ClientTest.php`](test/unit/ClientTest.php) file with unit tests as you modify the code.
 
 ```bash
 composer install
@@ -166,7 +166,7 @@ Please run your code through:
 5. Locally merge (or rebase) the upstream development branch into your topic branch:
 
    ```bash
-   git pull [--rebase] upstream master
+   git pull [--rebase] upstream main
    ```
 
 6. Push your topic branch up to your fork:
@@ -176,7 +176,7 @@ Please run your code through:
    ```
 
 7. [Open a Pull Request](https://help.github.com/articles/using-pull-requests/)
-    with a clear title and description against the `master` branch. All tests must be passing before we will review the PR.
+    with a clear title and description against the `main` branch. All tests must be passing before we will review the PR.
 
 <a name="code-reviews"></a>
 ## Code Reviews

README.md

@@ -1,6 +1,6 @@
-![SendGrid Logo](https://uiux.s3.amazonaws.com/2016-logos/email-logo%402x.png)
+![SendGrid Logo](twilio_sendgrid_logo.png)
 
-[![Travis Badge](https://travis-ci.org/sendgrid/php-http-client.svg?branch=master)](https://travis-ci.org/sendgrid/php-http-client)
+[![Travis Badge](https://travis-ci.org/sendgrid/php-http-client.svg?branch=main)](https://travis-ci.org/sendgrid/php-http-client)
 [![Latest Version on Packagist](https://img.shields.io/packagist/v/sendgrid/php-http-client.svg?style=flat-square)](https://packagist.org/packages/sendgrid/php-http-client)
 [![Email Notifications Badge](https://dx.sendgrid.com/badge/php)](https://dx.sendgrid.com/newsletter/php)
 [![Twitter Follow](https://img.shields.io/twitter/follow/sendgrid.svg?style=social&label=Follow)](https://twitter.com/sendgrid)
@@ -14,7 +14,7 @@ If you are looking for the SendGrid API client library, please see [this repo](h
 # Announcements
 **The default branch name for this repository has been changed to `main` as of 07/27/2020.**
 
-All updates to this library are documented in our [CHANGELOG](https://github.com/sendgrid/php-http-client/blob/master/CHANGELOG.md).
+All updates to this library are documented in our [CHANGELOG](CHANGELOG.md).
 
 # Table of Contents
 - [Installation](#installation)
@@ -172,14 +172,14 @@ If you are interested in the future direction of this project, please take a loo
 <a name="contribute"></a>
 # How to Contribute
 
-We encourage contribution to our libraries, please see our [CONTRIBUTING](https://github.com/sendgrid/php-http-client/blob/master/CONTRIBUTING.md) guide for details.
+We encourage contribution to our libraries, please see our [CONTRIBUTING](CONTRIBUTING.md) guide for details.
 
 Quick links:
 
-- [Feature Request](https://github.com/sendgrid/php-http-client/blob/master/CONTRIBUTING.md#feature-request)
-- [Bug Reports](https://github.com/sendgrid/php-http-client/blob/master/CONTRIBUTING.md#submit-a-bug-report)
-- [Improvements to the Codebase](https://github.com/sendgrid/php-http-client/blob/master/CONTRIBUTING.md#improvements-to-the-codebase)
-- [Review Pull Requests](https://github.com/sendgrid/php-http-client/blob/master/CONTRIBUTING.md#code-reviews)
+- [Feature Request](CONTRIBUTING.md#feature-request)
+- [Bug Reports](CONTRIBUTING.md#submit-a-bug-report)
+- [Improvements to the Codebase](CONTRIBUTING.md#improvements-to-the-codebase)
+- [Review Pull Requests](CONTRIBUTING.md#code-reviews)
 
 <a name="thanks"></a>
 # Thanks