Corrected README version

Author: tracyboehrer

README.md

@@ -18,7 +18,7 @@ For more information jump to a section below.
 
  | Branch | Description | Build Status | Coverage Status |
  |--------|-------------|--------------|-----------------|
- |Main | Preview 8 Builds | [![Build Status](https://travis-ci.org/Microsoft/botbuilder-java.svg?branch=main)](https://travis-ci.org/Microsoft/botbuilder-java) | [![Coverage Status](https://coveralls.io/repos/github/microsoft/botbuilder-java/badge.svg?branch=823847c676b7dbb0fa348a308297ae375f5141ef)](https://coveralls.io/github/microsoft/botbuilder-java?branch=823847c676b7dbb0fa348a308297ae375f5141ef) |
+ |Main | Preview 7 Builds | [![Build Status](https://travis-ci.org/Microsoft/botbuilder-java.svg?branch=main)](https://travis-ci.org/Microsoft/botbuilder-java) | [![Coverage Status](https://coveralls.io/repos/github/microsoft/botbuilder-java/badge.svg?branch=823847c676b7dbb0fa348a308297ae375f5141ef)](https://coveralls.io/github/microsoft/botbuilder-java?branch=823847c676b7dbb0fa348a308297ae375f5141ef) |
 
 ## Getting Started
 To get started building bots using the SDK, see the [Azure Bot Service Documentation](https://docs.microsoft.com/en-us/azure/bot-service/?view=azure-bot-service-4.0).