Update actions/checkout action to v2 (#63)

Co-authored-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

.github/workflows/npmpublish.yml

@@ -9,7 +9,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - uses: actions/setup-node@v1
         with:
           node-version: 12
@@ -20,7 +20,7 @@ jobs:
     needs: build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - uses: actions/setup-node@v1
         with:
           node-version: 12
@@ -33,7 +33,7 @@ jobs:
     needs: build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v2
       - uses: actions/setup-node@v1
         with:
           node-version: 12