appveyor install nsis from s3 (#3212)

* appveyor install nsis from s3

* Pass YAML linting, pls work

* Simpler nsis download scheme

.appveyor.yml

@@ -17,7 +17,8 @@ install:
   - call "%ProgramFiles(x86)%\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x86
   - set PATH=C:\Qt\Tools\QtCreator\bin;C:\Qt\5.5\msvc2013\bin;%PATH%
   - mkdir %LOCALAPPDATA%\QtProject && copy test\qtlogging.ini %LOCALAPPDATA%\QtProject\
-  - if "%CONFIG%" EQU "installer" ( cinst nsis.install -pre -y -installArgs /D="%programfiles(x86)%\NSIS" )
+  - ps: Start-FileDownload https://s3-us-west-2.amazonaws.com/qgroundcontrol/dependencies/nsis-3.0rc1-setup.exe -FileName nsis.exe
+  - nsis.exe /S
 
 build_script:
   - mkdir %SHADOW_BUILD_DIR% && cd %SHADOW_BUILD_DIR% && C:\Qt\5.5\msvc2013\bin\qmake -r CONFIG-=debug_and_release CONFIG+=%CONFIG% CONFIG+=WarningsAsErrorsOn %APPVEYOR_BUILD_FOLDER%\qgroundcontrol.pro