Update changelog (Azure#16154)

Author: lzchen

sdk/monitor/azure-opentelemetry-exporter-azuremonitor/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Release History
 
-## 1.0.0b2 (Unreleased)
+## 1.0.0b2 (2021-01-13)
 
   **Breaking Changes**
   - Rename Azure Trace exporter class, only allow connection string configuration
@@ -67,4 +67,4 @@
 
 ## 0.1a.0 (2019-11-06)
 
-- Initial alpha release
+- Initial alpha release