ci: add os matrix (#547)

Author: mdreizin

.github/workflows/dev.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        node: "14.x"
+        node: ["14.x"]
     steps:
       - name: Setup
         uses: actions/[email protected]