Fix release notes for release 7.31.0

release-notes/7-x.md

@@ -1,6 +1,8 @@
 # Release Notes for PROSE SDK versions 7.x
 
 ## [Release 7.31.0](https://www.nuget.org/packages/Microsoft.ProgramSynthesis/7.31.0) - 2021/05/25
+- General 
+    - **Refactored method signatures to avoid the use of nullable cancellation tokens for performance reasons (breaking change).**  
 - Transformation.Text
     - Added Translate telemetry event including translation duration, anonymized examples, and output expression.
     - Added a method to support the display or logging of masked confidential data (Microsoft.ProgramSynthesis.Transformation.Text.Example.ToPrivateString()). Upper case letters are converted to 'A', Lower case letters are converted to 'a', Numbers are converted to '9', Non-alphanumerics are preserved.