Use latest yarn version in the action

.github/workflows/master.yml

@@ -17,6 +17,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@master
+      - name: Install latest Yarn
+        run: npm install -g yarn
       - name: Print Yarn version
         run: yarn --version
       - name: Use Node.js ${{ env.NODE_VERSION }}