Added travis composer self-update

To try to avoid memory exhausted error on travis-ci I added a composer
self-update. Maybe it will resolve PHP 5.3 exhausted memory error.

Author: Flyers

.travis.yml

@@ -7,6 +7,7 @@ php:
 
 before_script:
   - phpenv config-rm xdebug.ini
+  - composer self-update
   - composer install
 
 script: phpunit -c app