travis: added HHVM nightly

Author: dg

.travis.yml

@@ -5,6 +5,7 @@ php:
     - 5.5
     - 5.6
     - hhvm
+    - hhvm-nightly
 
 env:
     - PHP_BIN=php
@@ -13,11 +14,15 @@ env:
 matrix:
     allow_failures:
         - php: hhvm
+        - php: hhvm-nightly
 
     exclude:
         - php: hhvm
           env: PHP_BIN=php-cgi
 
+        - php: hhvm-nightly
+          env: PHP_BIN=php-cgi
+
 script:
     - vendor/bin/tester -p $PHP_BIN tests -s
     - php code-checker/src/code-checker.php