Defined a new GIT_HASH environment variable which is a short hash generated from APPVEYOR_REPO_COMMIT

Author: end2endzone

appveyor.yml

@@ -32,6 +32,7 @@ image: Visual Studio 2015
 # scripts that are called at very beginning, before repo cloning
 init:
   - git config --global core.autocrlf true
+  - ps: $env:GIT_HASH=$env:APPVEYOR_REPO_COMMIT.Substring(0, 10)
 
 # fetch repository as zip archive
 shallow_clone: true                 # default is "false"