Mesa (12.0): appveyor: Force Visual Studio 2013 image.

[Jose Fonseca]

Module: Mesa
Branch: 12.0
Commit: 463d9ea0dc84c356e6208e00e15cf1b4c672f267
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=463d9ea0dc84c356e6208e00e15cf1b4c672f267

Author: Jose Fonseca <jfonseca at vmware.com>
Date:   Thu Aug 11 14:11:00 2016 +0100

appveyor: Force Visual Studio 2013 image.

It seems the default build image is now Visual Studio 2015, and Visual
Studio 2013 is not installed.

---

 appveyor.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/appveyor.yml b/appveyor.yml
index 2618f69..c2efa7e 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -37,6 +37,8 @@ cache:
 - win_flex_bison-2.4.5.zip
 - llvm-3.3.1-msvc2013-mtd.7z
 
+os: Visual Studio 2013
+
 environment:
   WINFLEXBISON_ARCHIVE: win_flex_bison-2.4.5.zip
   LLVM_ARCHIVE: llvm-3.3.1-msvc2013-mtd.7z