Added phpunit 4 to require-dev and using it in .travis.yml

Author: WyriHaximus

.travis.yml

@@ -14,4 +14,4 @@ before_script:
   - composer install --dev --prefer-source
 
 script:
-  - phpunit --coverage-text
+  - php vendor/bin/phpunit --coverage-text

composer.json

@@ -9,7 +9,8 @@
     },
     "require-dev": {
         "react/event-loop": "0.4.*",
-        "react/promise": "~2.0"
+        "react/promise": "~2.0",
+        "phpunit/phpunit": "4.*"
     },
     "suggest": {
         "react/event-loop": "0.4.*",