upgrade actions/checkout@v3 (#49)

Author: justjavac

.github/workflows/ci.yml

@@ -6,7 +6,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: actions/setup-node@v1
         with:
           node-version: 12