[TASK] Add PHP 7.1 and 7.2 to travis-ci

Minor phpunit upgrade from 4.7.x to 4.8.x to execute unit
tests with PHP 7.1 & 7.2 and still keep PHP 5.3

composer remove phpunit/phpunit
composer require --dev phpunit/phpunit ^4.8

Author: lolli42

.travis.yml

@@ -8,6 +8,8 @@ matrix:
     - php: 5.5
     - php: 5.6
     - php: 7
+    - php: 7.1
+    - php: 7.2
 
 sudo: false
 

composer.json

@@ -26,7 +26,7 @@
     "require-dev": {
         "composer/composer": "dev-master",
         "mikey179/vfsStream": "1.4.*@dev",
-        "phpunit/phpunit": "~4.7.0"
+        "phpunit/phpunit": "^4.8"
     },
     "replace": {
         "helhum/class-alias-loader": "*"