AppVeyor update

Author: ddmitov

appveyor.yml

@@ -1,6 +1,6 @@
 before_build:
   - set PATH=C:\Qt\5.9.5\msvc2015\bin;%PATH%
-  - "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" amd64
+  - \"C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat\" amd64
 
 build_script:
   - chdir %APPVEYOR_BUILD_FOLDER%\src