Android API level 21 backward compatibility? (Since the new update of the SDK came out)

I have a problem with the API Level 21. I want to use the Material Design and still be able to run the application on lower API levels like 18 (Android 4.3.1). But I always get that error:

My manifest SDK looks like that:

And the build.gradle like that:

Hope this is enougth information to get some help, I really need it :(

Cheers.