Update travis-ci environments.

hhvm-nightly is no more, but there is a php 7.0. Will it pass? The suspense is killing me!

.travis.yml

@@ -13,8 +13,8 @@ php:
   - 5.4
   - 5.5
   - 5.6
+  - 7.0
   - hhvm
-  - hhvm-nightly
 
 sudo: false