ci: set appveyor image

recp · recp · commit d5371f10a193 · 2017-04-22T15:17:36.000+03:00
diff --git a/appveyor.yml b/appveyor.yml
@@ -1,6 +1,7 @@
+image: Visual Studio 2017
+
 build_script:
 - ps: >-
     cd win
 
     .\build.bat
-
