Fix PHP 5.4 and 5.5 tests; drop HHVM support

.travis.yml

@@ -1,27 +1,27 @@
 language: php
 
 php:
-  - "5.4"
-  - "5.5"
   - "5.6"
   - "7.0"
   - "7.1"
   - "7.2"
   - "7.3"
-  - "hhvm"
 
 matrix:
   include:
     - php: 5.3
       dist: precise
+    - php: 5.4
+      dist: trusty
+    - php: 5.5
+      dist: trusty
 
 sudo: false
 
 install: travis_retry composer install --no-interaction --prefer-source
 
 script:
-  - if [ "$TRAVIS_PHP_VERSION" == "hhvm" ]; then vendor/bin/phpunit; fi
-  - if [ "$TRAVIS_PHP_VERSION" != "hhvm" ]; then vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover; fi
+  - vendor/bin/phpunit --coverage-text --coverage-clover=coverage.clover
 
 after_script:
-  - if [ "$TRAVIS_PHP_VERSION" != "hhvm" ] && [ "$TRAVIS_PHP_VERSION" != "7.0" ]; then vendor/bin/ocular code-coverage:upload --format=php-clover coverage.clover; fi
+  - if [ "$TRAVIS_PHP_VERSION" != "7.0" ]; then vendor/bin/ocular code-coverage:upload --format=php-clover coverage.clover; fi