Make appveyor build the release configuration.

Author: Idhrendur

appveyor.yml

@@ -5,7 +5,7 @@ build_script:
 - cmd: >-
     git submodule update --init --recursive
 
-    msbuild EU4ToVic2.sln /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
+    msbuild EU4ToVic2.sln -property:Configuration=Release /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
 test_script:
 - ps: vstest.console /logger:Appveyor frontend\Frontend.Core.Tests\bin\Release\Frontend.Core.Tests.dll
 artifacts: