Build using downloaded Qt

.appveyor.yml

@@ -45,7 +45,7 @@ install:
       Write-Host "Installed" -ForegroundColor Green
 
 build_script:
-  - mkdir %SHADOW_BUILD_DIR% && cd %SHADOW_BUILD_DIR% && C:\Qt\5.12.5\msvc2017_64\bin\qmake -r CONFIG+=%CONFIG% CONFIG+=WarningsAsErrorsOn %APPVEYOR_BUILD_FOLDER%\qgroundcontrol.pro
+  - mkdir %SHADOW_BUILD_DIR% && cd %SHADOW_BUILD_DIR% && C:\Qt-QGC-5.12.6\5.12.6\msvc2017_64\bin\qmake -r CONFIG+=%CONFIG% CONFIG+=WarningsAsErrorsOn %APPVEYOR_BUILD_FOLDER%\qgroundcontrol.pro
   - cd %SHADOW_BUILD_DIR% && jom
   - if "%CONFIG%" EQU "installer" ( copy %SHADOW_BUILD_DIR%\release\QGroundControl-installer.exe %APPVEYOR_BUILD_FOLDER%\QGroundControl-installer.exe )
 # Generate the source server information to embed in the PDB