Bump node.js version used in CI

Current LTS release is 20.x, and current (1.85) VSCode uses 18.x.

.github/workflows/npm-publish.yml

@@ -1,43 +1,42 @@
 name: Build
 
-on: 
-  push: 
+on:
+  push:
     branches:
       - master
-  pull_request: 
-    branches: 
+  pull_request:
+    branches:
       - master
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
 
     strategy:
       matrix:
-        node-version: [12.x, 14.x]
+        node-version: [18.x, 20.x]
 
     steps:
-    - uses: actions/checkout@v2
-    - name: Use Node.js ${{ matrix.node-version }}
-      uses: actions/setup-node@v1
-      with:
-        node-version: ${{ matrix.node-version }}
-    - run: npm install
-    - run: npm test
-      env:
-        CI: true
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm install
+      - run: npm test
+        env:
+          CI: true
 
   publish:
     needs: build
     runs-on: ubuntu-latest
     if: success() && github.ref == 'refs/heads/master'
     steps:
       - uses: actions/checkout@v2
-      - name: Use Node.js 12.x
+      - name: Use Node.js 18.x
         uses: actions/setup-node@v1
         with:
-          node-version: 12.x
+          node-version: 18.x
           registry-url: https://registry.npmjs.org/
       - run: npm install
       - run: npm publish --access public