7.0.0

This version of the rails gems supports Elasticsearch 7.0 and Rails 6.

It has the following changes in addition to those in release 7.0.0.pre

• [MODEL] Fix naming with inheritance when using Proxy (#887)
• [MODEL] Refactor module/mixin organization for clarity (#893)
• [MODEL] Only add the document_type to the request if it's defined (#894)
• [MODEL] Remove support for Single Table Inheritance (STI)
• Test Rails 6
• Remove unnecessary self as a return value of initialize method (#897