ci: use xcode12.2

.github/workflows/main.yml

@@ -2,6 +2,9 @@ name: ClashX
 
 on: [push]
 
+env:
+  DEVELOPER_DIR: /Applications/Xcode_12.2.app
+
 jobs:
   build:
     runs-on: macOS-latest
@@ -9,6 +12,7 @@ jobs:
     - uses: actions/checkout@v2
     - name: import certs
       run: |
+        echo `/usr/bin/xcodebuild -version`
         openssl aes-256-cbc -k  "${{ secrets.ENCRYPTION_SECRET }}" -in ".github/certs/dist.p12.enc" -d -a -out ".github/certs/dist.p12"
         gem install bundler:1.16.2
         bundle install