Try to fix AppVeyor build

Add workaround deploy script, described here:
http://help.appveyor.com/discussions/problems/8215-cannot-publish-to-nuget-get-400-bad-request-error

Author: angularsen

appveyor.yml

@@ -34,4 +34,8 @@ deploy:
   api_key:
     secure: 4E0S7bjDLDdCCLtRqD0mMXTg5pOwppHWS5C77acZ9HpvaN8rGmwn6ANfLrAUxxF+
   on:
-    branch: master
+    branch: master
+deploy_script:
+  - appveyor DownloadFile https://dist.nuget.org/win-x86-commandline/latest/nuget.exe
+  - ps: .\nuget.exe setApiKey %api_key% -source https://www.nuget.org | out-null
+  - ps: ($artifacts.values | Where-Object { $_.path -like '*.nupkg' }) | foreach-object {nuget.exe push $_.path -Source https://www.nuget.org/api/v2/package}