ci: Revert "ci: add testing for nodejs 6.x, 8.x, 10.x"

This reverts commit 2ef7ac8.

Author: oldskytree

.github/workflows/node.js.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [6.x, 8.x, 10.x, 12.x, 14.x, 16.x]
+        node-version: [12.x, 14.x, 16.x]
 
     steps:
     - uses: actions/checkout@v2
@@ -25,5 +25,5 @@ jobs:
       with:
         node-version: ${{ matrix.node-version }}
         cache: 'npm'
-    - run: npm install
+    - run: npm ci
     - run: npm test