GitHub workflow: update bazel mac image version
diff --git a/.github/workflows/bazel.yml b/.github/workflows/bazel.yml
index b11cea6..d151968 100644
--- a/.github/workflows/bazel.yml
+++ b/.github/workflows/bazel.yml
@@ -15,7 +15,7 @@
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04, macos-10.15]
+        os: [ubuntu-20.04, macos-11]
 
     steps:
       - uses: actions/checkout@v2