[appveyor] request the image that is intended for MinGW

diff --git a/appveyor.yml b/appveyor.yml
index 0355227..0c55d30 100644 (file)
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,6 +1,7 @@
 # This file is intended to automatize the testing of SimGrid on
 # Windows using the appveyor.com continuous integration service
 
+os: MinGW
 version: "{build}"
 clone_depth: 1