fix: bump up the Node.JS to v16

also update tsconfig.json to follow the recommendation in the wiki:
https://github.com/microsoft/TypeScript/wiki/Node-Target-Mapping#node-16

refs actions/runner#1439

.github/workflows/build.yml

@@ -16,10 +16,13 @@ jobs:
         with:
           # Make sure the release step uses its own credentials.
           persist-credentials: false
-      - name: Use Node.js v12.x
+      - name: Read .nvmrc
+        run: echo "##[set-output name=NVMRC;]$(cat .nvmrc)"
+        id: nvm
+      - name: Set up Node.js
         uses: actions/setup-node@v2
         with:
-          node-version: 12.x
+          node-version: "${{ steps.nvm.outputs.NVMRC }}"
           cache: npm
       - name: Build
         run: |

.github/workflows/test-with-tokens.yml

@@ -15,10 +15,13 @@ jobs:
       - uses: actions/checkout@v2
         with:
           ref: ${{ github.event.workflow_run.head_sha }}
-      - name: Use Node.js v12.x
+      - name: Read .nvmrc
+        run: echo "##[set-output name=NVMRC;]$(cat .nvmrc)"
+        id: nvm
+      - name: Set up Node.js
         uses: actions/setup-node@v2
         with:
-          node-version: 12.x
+          node-version: "${{ steps.nvm.outputs.NVMRC }}"
           cache: npm
       - name: Build
         run: |
@@ -36,4 +39,4 @@ jobs:
           name: test-with-tokens
           sha: ${{ github.event.workflow_run.head_sha }}
           conclusion: ${{ job.status }}
-          details_url : https://github.com/${{github.repository}}/actions/runs/${{github.run_id}}
+          details_url: https://github.com/${{github.repository}}/actions/runs/${{github.run_id}}

.nvmrc

@@ -1 +1 @@
-12
+16

action.yml

@@ -12,7 +12,7 @@ inputs:
     required: true
     description: The slug of target Read the Docs project
 runs:
-  using: "node12"
+  using: "node16"
   main: "dist/index.js"
 branding:
   icon: "book"