Update supported Xcode versions to fix Github Action failures. (#579)

* Update supported Xcode versions

* Switch from 12.0.1 to 12.0

* Add 12.2
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 6dc4ed4..009bdf2 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -20,7 +20,7 @@
       matrix:
         go: ['1.14', '1.15']
         os: ['macos-10.15']
-        xcode-version: ['12.0', '11.7', '11.6', '11.5', '11.4.1', '11.3.1', '11.2.1', '11.1', '11.0']
+        xcode-version: ['12.2', '12.1', '12.0', '11.7', '11.6', '11.5', '11.4.1', '11.3.1', '11.2.1']
     steps:
       - name: Update go version
         uses: actions/setup-go@v2