travis: Use gradle 5.1.1
travis: Use gradle 5.1.1

igniterealtime/Smack,igniterealtime/Smack,igniterealtime/Smack,Flowdalic/Smack,vanitasvitae/Smack,Flowdalic/Smack,vanitasvitae/Smack,Flowdalic/Smack,vanitasvitae/Smack