Avoid hiding nightly failures

.travis.yml

@@ -17,8 +17,6 @@ matrix:
         - php: 7.0
           env: deps=low
     fast_finish: true
-    allow_failures:
-        - php: nightly
 
 before_script:
   - echo "extension = redis.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini