Add caching for NodeJS

.github/workflows/tests.yml

@@ -93,9 +93,11 @@ jobs:
       uses: actions/checkout@v2
       
     - name: Setup Node
-      uses: actions/setup-node@v1
+      uses: actions/setup-node@v2
       with:
         node-version: '12'
+        cache: 'npm'
+        cache-dependency-path: 'js/package-lock.json'
         
     - name: Setup Mocha
       run: npm install -g mocha