See http://getcomposer.org/doc/articles/troubleshooting.md#package-not-found-on-travis-ci-org.

whatthejeff · whatthejeff · commit 455a413d4159 · 2013-06-22T23:56:03.000-04:00
diff --git a/.travis.yml b/.travis.yml
@@ -5,7 +5,7 @@ php:
     - 5.5
 
 before_script:
-    - composer install --dev --prefer-source
+    - COMPOSER_ROOT_VERSION=dev-master composer install --dev --prefer-source
 
 script: vendor/bin/phpunit --configuration ./build/travis-ci.xml
 
