Using project.configurations.create instead of project.configurations.add

Pull requires to avoid the following warning when using the ScalaStyle plugin with Gradle version >= 1.6:
```The ConfigurationContainer.add() method has been deprecated and is scheduled to be removed in Gradle 2.0. Please use the create() method instead.```

* http://www.gradle.org/docs/1.6/release-notes#renamed-several-add()-methods