build.gradle: Update jxmpp javadoc link
build.gradle: Update jxmpp javadoc link

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