Change diff coverage threshold to 80% (#123)

Change code diff coverage threshold to 80%

Author: liuh-80

azure-pipelines.yml

@@ -20,7 +20,7 @@ stages:
     displayName: "build"
     timeoutInMinutes: 60
     variables:
-      DIFF_COVER_CHECK_THRESHOLD: 50
+      DIFF_COVER_CHECK_THRESHOLD: 80
       DIFF_COVER_ENABLE: 'true'
     pool:
       vmImage: ubuntu-20.04