Bump up the action/cache version

Author: cschreib

.github/workflows/cmake.yml

@@ -39,7 +39,7 @@ jobs:
     - name: Setup Emscripten cache
       if: matrix.platform.compiler == 'em++'
       id: cache-system-libraries
-      uses: actions/cache@v2
+      uses: actions/cache@v2.1.7
       with:
         path: ${{env.EM_CACHE_FOLDER}}
         key: ${{env.EM_VERSION}}-${{ runner.os }}