Use VS2017 AppVeyor image

Daniel15 · Daniel15 · commit 03625267e21f · 2017-05-08T22:23:58.000-07:00
diff --git a/appveyor.yml b/appveyor.yml
@@ -1,5 +1,5 @@
 version: '{build}'
-os: Visual Studio 2015
+os: Visual Studio 2017
 install:
 - set PATH=%ProgramFiles(x86)%\MSBuild\14.0\Bin;%PATH%
 build:
