cache node dependencies

.github/workflows/main.yml

@@ -19,6 +19,19 @@ jobs:
       with:
         node-version: ${{ matrix.node-version }}
 
+    - name: Get yarn cache directory path
+      id: yarn-cache-dir-path
+      run: echo "::set-output name=dir::$(yarn cache dir)"
+
+    - name: Restore yarn cache directory
+      uses: actions/cache@v2
+      id: yarn-cache # use this to check for `cache-hit` (`steps.yarn-cache.outputs.cache-hit != 'true'`)
+      with:
+        path: ${{ steps.yarn-cache-dir-path.outputs.dir }}
+        key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+        restore-keys: |
+          ${{ runner.os }}-yarn-
+
     - name: Install dependencies
       run: yarn install