ga: fix os syntax
diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index 6f6c4d3..d6ed545 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -3,8 +3,11 @@
 
 jobs:
   all:
-#    runs-on: [ ubuntu-latest, windows-latest, macos-latest ]
-    runs-on: [ ubuntu-latest, macos-latest ]
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+#        os: [macos-latest, ubuntu-latest, windows-latest]
+        os: [macos-latest, ubuntu-latest]
     steps:
       - name: checkout
         uses: actions/checkout@v2