Add latest Node versions to CI (#18)

Author: denis-sokolov

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [6.x, 8.x, 10.x, 11.x, 12.x, 13.x]
+        node-version: [6.x, 8.x, 10.x, 11.x, 12.x, 13.x, 14.x, 15.x]
     steps:
     - uses: actions/checkout@v2
     - name: Use Node.js ${{ matrix.node-version }}