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

[Jose Fonseca]

Module: Mesa
Branch: master
Commit: 06b63f1f43fd11c9bbf4fe6d6699de27d4022a85
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=06b63f1f43fd11c9bbf4fe6d6699de27d4022a85

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