Merge pull request #1 from erikmd/use-underscores

Use underscores

Author: erikmd

.github/workflows/build-coq-demo.yml

@@ -25,6 +25,6 @@ jobs:
     - uses: erikmd/docker-coq-action@alpha
       id: docker-coq-action
       with:
-        opam-file: 'coq-demo.opam'
-        coq-version: '8.11'
-        ocaml-version: '4.07-flambda'
+        opam_file: 'coq-demo.opam'
+        coq_version: '8.11'
+        ocaml_version: '4.09-flambda'