erlang-xmpp: Update to 1.6.0

upstream changes:
-----------------
Version 1.6.0
  o Updating fast_tls to version 1.1.16.
  o Updating stringprep to version 1.0.29.
  o Support additional namespaces in MIX elements
  o Add support for MIX presences, update_subscriptions and unsubscribe
  o Add allow_query_users to muc config
Version 1.5.8
  o Updating fast_tls to version 1.1.15.
  o Updating ezlib to version 1.0.12.
Version 1.5.7
  o Updating ezlib to version 1.0.11.
  o Updating fast_tls to version 1.1.14.
  o Updating fast_xml to version 1.1.49.
  o Updating stringprep to version 1.0.28.
  o Updating p1_utils to version 1.0.25.
  o Make socket release on detach, free resources earlier
  o Fix crash when doing srv resolution
Version 1.5.6
  o Updating fast_xml to version 1.1.48.
Version 1.5.5
  o Updating fast_xml to version 1.1.47.
  o Allow 'max' value in pubsub max_items, item_expire and children_max
  o Add compatibility quirk for old smack version in roster
  o Don't generate code attribute in errors (deprececed by rfc6120)
  o Change internal representation of markable element
  o Add MUC hats support
  o Generate documentation before publishing to hex
Version 1.5.4
  o Updating ezlib to version 1.0.10.
  o Updating fast_tls to version 1.1.13.
  o Updating fast_xml to version 1.1.47.
  o Updating stringprep to version 1.0.27.
  o Updating p1_utils to version 1.0.23.
  o Switch from using Travis to Github Actions as CI
  o Add support for MIX roster extension
  o Allow children inside address element
  o Make compatible with OTP24
  o Allow arbitrary children inside vCard

(triaxx)