Add more OS and node versions

Author: darkriszty

.github/workflows/test.yml

@@ -8,14 +8,19 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        node-version: [ '12.x', '14.x', '15.x' ]
 
     steps:
     - uses: actions/checkout@v2
     - name: Use Node.js ${{ matrix.node-version }}
       uses: actions/setup-node@v1
       with:
-        node-version: 15.x
+        node-version: ${{ matrix.node-version }}
 
     - run: npm ci
     - run: npm test