Update prosody modules to include the latest mod_block_strangers

src/freedombone-app-xmpp

 prosody_nightly_url="https://prosody.im/nightly/${prosody_latest_version}/latest/${prosody_filename}.tar.gz"
 
 # From https://hg.prosody.im/prosody-modules
-prosody_modules_filename='prosody-modules-20180322.tar.gz'
-prosody_modules_hash='982d0dfcef98e9cb9cee4cc3801b8ce9a503a32e44c32b99df6fe94545b90072'
+prosody_modules_filename='prosody-modules-20180602.tar.gz'
+prosody_modules_hash='c8ea99a3c9ed25e6471cd7de991a58715f1478e3bf3c5866b9f34a9ef8a863dd'
 xmpp_encryption_warning=$"For security reasons, OMEMO or PGP encryption is required for conversations on this server."
 
 XMPP_SHORT_DESCRIPTION=$'Chat system'