Enable CI

.github/workflows/ci.yml

@@ -1,9 +1,9 @@
 name: "CI"
-on: # rebuild any PRs and main branch changes
+on:
   pull_request:
   push:
     branches:
-      - master
+      - main
       - 'releases/*'
 
 jobs:
@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest]
+        os: [ubuntu-latest, macOS-latest, windows-latest]
     steps:
     - uses: actions/checkout@v2
     - run: |