Enable TravisCI testing on PHP 7.1, 7.2 and nightly

Author: mondrake

.travis.yml

@@ -9,10 +9,14 @@ php:
     - 5.5
     - 5.6
     - 7.0
+    - 7.1
+    - 7.2
+    - nightly
     - hhvm
 
 matrix:
   allow_failures:
+    - php:nightly
     - php: hhvm
   fast_finish: true