Crouton depends on libraries but is not a library itself

This issue due to com.android.support-v4 recent update.

So I changed

compile 'com.android.support:support-v4:20.+'

to

compile 'com.android.support:support-v4:19.1.+'

and crouton works fine

Different workaround is to use @aar:

compile('de.keyboardsurfer.android.widget:crouton:1.8.4@aar') {
    exclude group: 'com.google.android', module: 'support-v4'
}