Fixed broken link in ACS Common README.
This package contains common code for Azure Communication Service libraries.
[Source code](https://github.com/Azure/azure-sdk-for-android/tree/master/sdk/communication/azure-communication-common)
-| [API reference documentation](https://azure.github.io/azure-sdk-for-android/sdk/communication/azure-communication-common/azure-communication-common/index.html)
+| [API reference documentation](https://azure.github.io/azure-sdk-for-android/azure-communication-common/index.html)
| [Product documentation](https://docs.microsoft.com/azure/communication-services/overview)
## Getting started
