Update appveyor.yml

appveyor.yml

@@ -7,6 +7,7 @@ environment:
 build_script:
   - git config --global user.name "purerosefallen"
   - git config --global user.email "78877@qq.com"
+  - git checkout master
   - git clone https://github.com/purerosefallen/ygopro-222DIY
   - cd ygopro-222DIY