[REEF-1634] Add AppVeyor build for VS2013

JIRA:
  [REEF-1634](https://issues.apache.org/jira/browse/REEF-1634)

Pull request:
  This closes #1150
diff --git a/appveyor.yml b/appveyor.yml
index 000c86e..21b158c 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -17,6 +17,10 @@
 
 shallow_clone: true
 
+os:
+ - Visual Studio 2013
+ - Visual Studio 2015
+
 platform: x64
 configuration: Debug