chore: run all GH actions using Node LTS, not v12

Author: SimenB

.github/workflows/doctoc.yml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v3
         with:
-          node-version: '12.x'
+          node-version: 'lts/*'
       - name: Install doctoc
         run: npm i -g doctoc
       - name: Create README copy and diff with doctoc

.github/workflows/eclint.yml

@@ -9,6 +9,6 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v3
         with:
-          node-version: '12.x'
+          node-version: 'lts/*'
       - run: npm i -g eclint
       - run: eclint check

.github/workflows/markdown-link-check.yml

@@ -12,7 +12,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v3
         with:
-          node-version: '12.x'
+          node-version: 'lts/*'
       - name: Install markdown-link-check
         run: npm i -g markdown-link-check
       - name: Run markdown-link-check on MD files