Add PHP 7.3 to Travis, remove HHVM

Author: StudioMaX

.travis.yml

@@ -1,22 +1,19 @@
 language: php
 
 php:
-  - 5.5
   - 5.6
   - 7.0
   - 7.1
   - 7.2
-  - hhvm
+  - 7.3
   - nightly
 
-sudo: false
-
 matrix:
+  include:
+    - php: 5.5
+      dist: trusty
   allow_failures:
-    - php: hhvm
-
-before_install:
-    - composer self-update
+    - php: nightly
 
 install:
     - composer require "php-http/guzzle6-adapter:^1.0" --no-update