Try to fix the VCS tests: git commit on windows

Needs extra (fake) config to be supplied on the command line otherwise
it complains it doesn't know the author name or email.

Author: dcoutts

cabal-install/tests/UnitTests/Distribution/Client/VCS.hs

@@ -624,8 +624,10 @@ vcsTestDriverGit verbosity vcs repoRoot =
         git ["add", filename]
 
     , vcsCommitChanges = \_state -> do
-        git $ ["commit", "--all", "--message=a patch",
-               "--author=Author <[email protected]>"] ++ verboseArg
+        git $ [ "-c", "user.name", "A", "-c", "user.email", "[email protected]"
+              , "commit", "--all", "--message=a patch",
+              , "--author=A <[email protected]>"
+              ] ++ verboseArg
         commit <- git' ["log", "--format=%H", "-1"]
         let commit' = takeWhile (not . isSpace) commit
         return (Just commit')