Configure Travis CI to run PSR-2 code style checks

Also configures Gitter integration.

framework/core/.travis.yml

@@ -1,12 +1,27 @@
 language: php
 
 php: 
-  - 5.3
   - 5.4
   - 5.5
+  - 5.6
+  - hhvm
+
+matrix:
+  allow_failures:
+    - php: hhvm
+  fast_finish: true
 
 before_script:
   - curl -s http://getcomposer.org/installer | php
-  - php composer.phar install --dev
+  - php composer.phar install
 
-script: phpunit
+script:
+  - vendor/bin/phpcs --standard=PSR2 -np src
+
+notifications:
+  webhooks:
+    urls:
+      - https://webhooks.gitter.im/e/7b9e9827a03b44a16588
+    on_success: always
+    on_failure: always
+    on_start: false