javadocAll: Set source to sourceCompatibility to work around bug
javadocAll: Set source to sourceCompatibility to work around bug

in JDK 11. See https://bugs.openjdk.java.net/browse/JDK-8217177

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