I\'d like to learn how to use Android Studio at the best, but I still have limited experience especially in building with Gradle.
This appears to be a bug in the Android Gradle plugin and not something you're doing wrong; I see it coming up any time you include a dependency in one of your modules even if it's specified correctly. This warning isn't anything to worry about.
I've filed https://code.google.com/p/android/issues/detail?id=65501 about this.