CI: Use checkout@v2 (microsoft#38822)

Author: imba-tjd

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
         node-version: [10.x, 12.x, 13.x]
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
       with:
         fetch-depth: 5
     - name: Use node version ${{ matrix.node-version }}
@@ -45,4 +45,4 @@ jobs:
 
     - name: Validate the browser can import TypeScript
       run: gulp test-browser-integration
-    
+