Drop support for PHP 5.5 and 5.6

Author: vladsandu

.travis.yml

@@ -1,15 +1,16 @@
 language: php
-sudo: false
+
+dist: xenial
+
 php:
-- 5.5
-- 5.6
 - 7.0
 - 7.1
 - 7.2
 - 7.3
 - 7.4
-dist: trusty
+
 before_script:
 - composer self-update
 - composer install --no-interaction
+
 script: composer test

composer.json

@@ -7,11 +7,11 @@
     "license": "MIT",
     "description": "The officially supported client for Postmark (http://postmarkapp.com)",
     "require": {
-        "php": ">=5.5.0",
+        "php": ">=7.0.0",
         "guzzlehttp/guzzle": "^6.0|^7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.0|^6.0"
+        "phpunit/phpunit": "^6.0.0"
     },
     "autoload": {
         "psr-0": {