patch 9.0.0522: build fails on Appveyor

Problem:    Build fails on Appveyor.
Solution:   Select Visual Studio 2015 for the build tools.

.appveyor.yml

@@ -17,6 +17,8 @@ matrix:
 before_build:
   # Use Windows SDK 7.1 (= MSVC 2010)
   - '"C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd" /x64 /release'
+  # Visual Studio 2015 compiler tools
+  - '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86_amd64'
   - 'set INCLUDE=%INCLUDE%C:\Program Files (x86)\Windows Kits\8.1\Include\um'
 
 build_script:

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    522,
 /**/
     521,
 /**/