fixed travis hhvm problem

.travis.yml

@@ -1,15 +1,29 @@
 language: php
-php:
-  - 5.3
-  - 5.4
-  - 5.5
-  - 5.6
-  - 7.0
-  - 7.1
-  - hhvm
+sudo: false
+
+cache:
+    directories:
+      - $HOME/.composer/cache/files
 
 before_script:
-  - composer self-update
-  - composer install --no-interaction --prefer-source --dev
-
-script: vendor/bin/phpunit
+    - composer self-update
+    - composer install --no-interaction --prefer-source --dev
+
+script: ./vendor/bin/phpunit
+
+matrix:
+    include:
+        - php: 5.3
+        - php: 5.4
+        - php: 5.5
+        - php: 5.6
+        - php: 7.0
+        - php: 7.1
+        - php: hhvm-3.18
+          sudo: required
+          dist: trusty
+          group: edge
+
+cache:
+    directories:
+        - .phpunit