Update to be in-line with composer docs.

.travis.yml

@@ -6,7 +6,7 @@ php:
   - 5.5
 
 before_script:
-  - composer selfupdate && composer --version
+  - composer self-update && composer --version
   - composer require satooshi/php-coveralls 0.6.*
   - mysql -e 'CREATE DATABASE yiitest;';
   - psql -U postgres -c 'CREATE DATABASE yiitest;';