Add php-nightly to Travis-CI

Signed-off-by: Maurício Meneghini Fauth <mauriciofauth@gmail.com>

.travis.yml

@@ -18,6 +18,7 @@ php:
   - "5.5"
   - "hhvm-3.12"
   - "hhvm-3.18"
+  - "nightly"
 
 sudo: required
 
@@ -81,6 +82,10 @@ matrix:
         - ln -s "`pwd`/composer.phar" /usr/local/bin/composer
         - mysql.server start
 
+  allow_failures:
+    - php: "nightly"
+      env: CI_MODE=test
+
 cache:
   pip: true
   directories: