Added VS2017 to AppVeyor matrix
diff --git a/appveyor.yml b/appveyor.yml
index 6576baf..53ea97a 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -9,6 +9,7 @@
 os:
   - Visual Studio 2013
   - Visual Studio 2015
+  - Visual Studio 2017
 
 init:
   - git config --global core.autocrlf input