build(node): update node from 4.1.1 to 4.2.1

This is just a maintenance upgrade to keep us close to the latest release.

No known bugs are being fixed by this upgrade.

I also removed the npm override in .travis.yaml since node 4 ships with a recent version of npm
and usually this version is preferred (it might contain custom patches).

Closes angular#4939

.nvmrc

@@ -1 +1 @@
-4.2
+4.2.1

.travis.yml

@@ -1,7 +1,7 @@
 language: node_js
 sudo: false
 node_js:
-- '4.1.1'
+- '4.2.1'
 
 branches:
   except:
@@ -60,9 +60,6 @@ before_install:
 - '[ "${TRAVIS_PULL_REQUEST}" = "false" ] && [ "${TRAVIS_BRANCH}" = "master" ] && SAUCE_USERNAME="angular2-ci" && SAUCE_ACCESS_KEY="693ebc16208a-0b5b-1614-8d66-a2662f4e" || true'
 
 install:
-  # Update npm
-  - npm install -g npm@2.14.5
-  - npm --version
   # Check the size of caches
   - du -sh ./node_modules || true
   # Install npm dependecies

DEVELOPER.md

@@ -36,9 +36,9 @@ following products on your development machine:
   [Windows](http://windows.github.com)); [GitHub's Guide to Installing
   Git](https://help.github.com/articles/set-up-git) is a good source of information.
 
-* [Node.js](http://nodejs.org), (version `>=4.1.1 <5`) which is used to run a development web server, 
+* [Node.js](http://nodejs.org), (version `>=4.2.1 <5`) which is used to run a development web server, 
   run tests, and generate distributable files. We also use Node's Package Manager, `npm` 
-  (version `>=2.14.5 <3.0`), which comes with Node. Depending on your system, you can install Node either from 
+  (version `>=2.14.7 <3.0`), which comes with Node. Depending on your system, you can install Node either from 
   source or as a pre-packaged bundle.
 
 * [Chrome Canary](https://www.google.com/chrome/browser/canary.html), a version of Chrome with

gulpfile.js

@@ -47,8 +47,8 @@ var sauceConf = require('./sauce.conf');
 var os = require('os');
 
 require('./tools/check-environment')({
-  requiredNpmVersion: '>=2.14.5',
-  requiredNodeVersion: '>=4.1.1'
+  requiredNpmVersion: '>=2.14.7',
+  requiredNodeVersion: '>=4.2.1'
 });
 
 // Make it easy to quiet down portions of the build.