[core-http] Update changelog for June 2020 release (Azure#9185)

Author: jeremymeng

sdk/core/core-http/CHANGELOG.md

@@ -1,8 +1,9 @@
 # Release History
 
-## 1.1.3 (Unreleased)
+## 1.1.3 (2020-06-02)
 
 - Fix issue of `SystemErrorRetryPolicy` didn't retry on errors [PR #8803](https://github.com/Azure/azure-sdk-for-js/pull/8803)
+- Add support for serialization of text media type. [PR #8977](https://github.com/Azure/azure-sdk-for-js/pull/8977)
 
 ## 1.1.2 (2020-05-07)