Run tests on windows, mac & ubuntu

.github/workflows/nodejs.yml

@@ -3,13 +3,14 @@ name: Test template output
 on: [push]
 
 jobs:
-  build:
-
-    runs-on: ubuntu-latest
-
+  test:
+    name: Test on node ${{ matrix.node_version }} and ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    
     strategy:
       matrix:
         node-version: [8.x, 10.x, 12.x]
+        os: [ubuntu-latest, windows-latest, macOS-latest]
 
     steps:
     - uses: actions/checkout@v1
@@ -17,7 +18,8 @@ jobs:
       uses: actions/setup-node@v1
       with:
         node-version: ${{ matrix.node-version }}
-    - name: npm install and test
+        
+    - name: npm install & test
       run: |
         npm install
         npm test