deprecate unsupported php versions

.travis.yml

 language: php
 
 php:
-  - 5.5
   - 5.6
   - 7
-  - hhvm
 
 matrix:
   fast_finish: true
-  allow_failures:
-    - php: hhvm
 
 sudo: false
 
@@ -35,4 +31,4 @@ script:
   - vendor/bin/phpunit --coverage-clover build/logs/clover.xml
 
 after_success:
-  - sh -c 'if [ "$TRAVIS_PHP_VERSION" != "hhvm" ]; then php vendor/bin/coveralls -v; fi;'
+  - sh -c 'php vendor/bin/coveralls -v'