Bump actions/checkout and add manual triggering

Author: mxie

.github/workflows/test.yml

@@ -1,5 +1,6 @@
 name: Test
 on:
+  workflow_dispatch:
   push:
     paths:
     - '**.js'
@@ -8,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v1
+      uses: actions/checkout@v2
     - name: Run Action
       uses: ./
       with: