Matrix test go versions

.github/workflows/ci.yml

@@ -10,6 +10,9 @@ jobs:
 
   ci:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        go: [ '', '1.x' ] # '' uses go.mod, 1.x uses latest go
     steps:
     - uses: actions/checkout@v2
       with:
@@ -18,7 +21,8 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: "1.x"
+        go-version-file: 'go.mod'
+        go-version: ${{ matrix.go }}
         stable: true
         check-latest: true