Release 1.5.6

Notable changes:

• Issue 1382 - WebSocketClient.upgradeSocketToSSL is enforcing TLS 1.2 (PR 1387)
• Issue 1390 - Thread created by NamedThreadFactory should be a daemon (PR 1391)

Check out the changelog and the milestone for more information.

A special thanks to all the contributors of this release:
@pavel-treutner
@PhilipRoman