Get Travis CI to ignore external library?

I have added dropboxChooserSDK library to my project as a plug-in. Now Travis is trying to build a library and it fails.

Is there a way to ignore the library?

My project structure looks like this:

• application
• build
• dropboxChooserSDK
• gradle

Error from Travis:

FAILURE: Build failed with exception.

Something went wrong:

• There was a problem setting up project ': app'.
• There was a problem setting up project ': dropboxChooserSDK'. could not find Build Tools version 19.1.0