Dropped HHVM test

Hoping nobody's mad about it. Too many issues cropping up with trying to get it testing and I'm not familiar enough with it to quickly get it resolved

.travis.yml

@@ -4,13 +4,23 @@ sudo: required
 
 matrix:
   include:
-    - php: hhvm
+    - php: 5.3
+      dist: precise
+    - php: 5.4
+      dist: trusty
+    - php: 5.5
+      dist: trusty
+    - php: 5.6
+      dist: trusty
+    - php: 7.0
       dist: xenial
-      env: HHVM=true PHPUNIT=5.7
+      env: PHPUNIT=5.7
+    - php: 7.1
+    - php: 7.2
+    - php: 7.3
 
 install:
   - composer install
-  - if [[ $HHVM == true ]]; then composer require "symphony/yaml:3.0"; fi
   - if [[ $PHPUNIT == 5.7 ]]; then composer require "phpunit/phpunit:5.7"; fi
 
 before_script: