sync Go version used in GitHub actions to 1.15.15 (#429)

* sync Go version used in GitHub actions to 1.15.15

* fix go mod tidy version

.github/workflows/nightly-build.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up Go 1.x
         uses: actions/setup-go@v2
         with:
-          go-version: ^1.15
+          go-version: ~1.15.15
         id: go
 
       #Need to install rpm so ubuntu can make rpm by default ubuntu can make deb