Use GeneratePackageOnBuild to create nupkg.

.appveyor.yml

@@ -4,6 +4,7 @@ platform: Any CPU
 environment:
   JAVA_HOME: '%ProgramFiles%\Java\jdk1.8.0'
   GRADLE_OPTS: '-Dorg.gradle.internal.launcher.welcomeMessageEnabled=false -Dorg.gradle.daemon=false'
+  GeneratePackageOnBuild: true
 cache:
   - '%ProgramData%\chocolatey\bin -> .appveyor.yml'
   - '%ProgramData%\chocolatey\lib -> .appveyor.yml'
@@ -17,7 +18,6 @@ before_build:
   - ps: gitversion /l console /output buildserver /updateprojectfiles DotNet
 build:
   project: DotNet\CesiumLanguageWriter.sln
-  publish_nuget: true
   parallel: true
   verbosity: minimal
 after_build: