Prepare version 5.2.0 (RolifyCommunity#478)

* Prepare version 5.2.0

* Upgrade database_cleaner for ruby 2.3 compatibility.

Version: 5.1.0

Version 5.0.0

Version v4.1.1

Version v4.1.0

Version 4.0.0

Version 3.5.2

Version 3.5.1

Version 3.5.0

Version 3.4.1