Fix verbosity of git

The lack of parenthesis in this line meant that we'd only see the
verbose output from git when we had a `peerLocalDir`.

This should fix verbosity of git

Author: alt-romes

cabal-install/src/Distribution/Client/VCS.hs

@@ -638,9 +638,9 @@ vcsGit =
           ["clone" ]
             ++ depthIs1
             ++ [ "--no-checkout", loc, localDir]
-            ++ case peer of
+            ++ (case peer of
               Nothing -> []
-              Just peerLocalDir -> ["--reference", peerLocalDir]
+              Just peerLocalDir -> ["--reference", peerLocalDir])
             ++ verboseArg
           where
             loc = srpLocation