Update workflow to more recent golang versions

.github/workflows/main.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go: ["1.13.x", "1.14.x", "1.15.x"]
+        go: ["1.15.x", "1.16.x", "1.17.x"]
     steps:
       - name: Checkout
         uses: actions/checkout@v2