updated the appveyor yml file to only build master for the main CI bulid

Author: Michael Hallett

appveyor.yml

@@ -1,15 +1,17 @@
-version: 105.0.1.{build}
-before_build:
-- nuget restore RestSharp.sln
-- appveyor RegisterXamarinLicense -Email %xamarin_email% -Password %xamarin_password% -Product Android
-- appveyor RegisterXamarinLicense -Email %xamarin_email% -Password %xamarin_password% -Product iOS
-build:
-  project: RestSharp.sln
-  verbosity: minimal
-after_build:
-- appveyor UnregisterXamarinLicense -Email %xamarin_email% -Password %xamarin_password%
-environment:
-  xamarin_email:
-    secure: zM9+mVyEGu7yKbL64GG5h0ulFnmt6/jfq8jynL2yCOw=
-  xamarin_password:
+version: 105.0.1.{build}
+before_build:
+- nuget restore RestSharp.sln
+- appveyor RegisterXamarinLicense -Email %xamarin_email% -Password %xamarin_password% -Product Android
+- appveyor RegisterXamarinLicense -Email %xamarin_email% -Password %xamarin_password% -Product iOS
+branches:
+  only:
+  - masterbuild:
+  project: RestSharp.sln
+  verbosity: minimal
+after_build:
+- appveyor UnregisterXamarinLicense -Email %xamarin_email% -Password %xamarin_password%
+environment:
+  xamarin_email:
+    secure: zM9+mVyEGu7yKbL64GG5h0ulFnmt6/jfq8jynL2yCOw=
+  xamarin_password:
     secure: sRp5YM8LTyje4swi/8p5tQ==