Cache yarn deps

.github/workflows/ci.yml

           node-version: 12.x
       - name: Install yarn
         run: npm install -g yarn
+      - name: Get yarn cache
+        id: yarn-cache
+        run: echo "::set-output name=dir::$(yarn cache dir)"
+      - uses: actions/cache@v1
+        with:
+          path: ${{ steps.yarn-cache.outputs.dir }}
+          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-yarn-
       - name: Install dependencies
         run: yarn install
       - name: Run tests
           node-version: 12.x
       - name: Install yarn
         run: npm install -g yarn
+      - name: Get yarn cache
+        id: yarn-cache
+        run: echo "::set-output name=dir::$(yarn cache dir)"
+      - uses: actions/cache@v1
+        with:
+          path: ${{ steps.yarn-cache.outputs.dir }}
+          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-yarn-
       - name: Install dependencies
         run: yarn install
       - name: Build android example app
         run: gem install cocoapods
       - name: Install yarn
         run: npm install -g yarn
+      - name: Get yarn cache
+        id: yarn-cache
+        run: echo "::set-output name=dir::$(yarn cache dir)"
+      - uses: actions/cache@v1
+        with:
+          path: ${{ steps.yarn-cache.outputs.dir }}
+          key: ${{ runner.os }}-yarn-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-yarn-
       - name: Install dependencies
         run: yarn install
       - name: Install pods