Moves PHP minimum PHP version to 5.5

Author: sagikazarmark

.travis.yml

@@ -1,7 +1,6 @@
 language: php
 
 php:
-  - 5.4
   - 5.5
   - 5.6
   - 7.0
@@ -12,7 +11,7 @@ matrix:
     - php: 7.0
     - php: hhvm
   include:
-    - php: 5.4
+    - php: 5.5
       env:
         - COMPOSER_FLAGS="--prefer-stable --prefer-lowest"
         - PHPUNIT_FLAGS="--coverage-clover build/coverage.xml"