fixed spelling mistake in feature request template file

Author: Nishara Ramasinghe

.github/ISSUE_TEMPLATE/feature_request.md

@@ -6,7 +6,7 @@ about: Suggest an idea for this project
 
 ## To-do (Overall work needs to be done)
 
-## Expected Behvior 
+## Expected Behaviour 
 
 ## Impact