Update changelog

Author: Kapil Borle

CHANGELOG.MD

@@ -1,6 +1,12 @@
 ## [unreleased](https://github.com/PowerShell/PSScriptAnalyzer/tree/development)
 ### Fixed
 - Regular expression in `target` parameter in SuppressMessageAttribute (#638)
+- Filtering on severity level for DSC rules (#642)
+- PSUseCompatibleCmdlets rule
+    + to check for commands in Microsoft.PowerShell.Core snapin
+    + to ignore aliases
+    + to ignore custom defind commands
+
 
 ## [1.8.1](https://github.com/PowerShell/PSScriptAnalyzer/tree/1.8.1) - 2016-10-13
 ### Added