Fix CI that has been broken on Windows. (#148)

* Update ci.yml

* Update ci.yml

* See how well cache works.

* test cache again

Co-authored-by: Cristiano Calcagno <[email protected]>

Author: chenglou

.github/workflows/ci.yml

@@ -25,9 +25,9 @@ jobs:
         key: ${{matrix.os}}-latest-ocaml-4.06.1
 
     - name: Use OCaml
-      uses: avsm/setup-ocaml@v1.1.10
+      uses: avsm/setup-ocaml@v2
       with:
-        ocaml-version: 4.06.1
+        ocaml-compiler: 4.06.x
 
     - name: Use Node.js
       uses: actions/[email protected]