Drop PHP 5.4 and HHVM

Author: GrahamCampbell

.travis.yml

@@ -1,20 +1,5 @@
 matrix:
   include:
-    - dist: trusty
-      language: php
-      php: hhvm-3.18
-      install: travis_retry composer install --no-suggest --prefer-dist -n -o
-      script: vendor/bin/phpunit
-    - dist: trusty
-      language: php
-      php: hhvm-3.30
-      install: travis_retry composer install --no-suggest --prefer-dist -n -o
-      script: vendor/bin/phpunit
-    - dist: trusty
-      language: php
-      php: 5.4
-      install: travis_retry composer install --no-suggest --prefer-dist -n -o
-      script: vendor/bin/phpunit
     - dist: trusty
       language: php
       php: 5.5.9