fix some mixed space+tab indentation

This fixes all instances of " \t" in the code base. Most common case
seems to be after a "where" line; probably vim copied the two space layout
of that line.

Done as a background task while listening to episode 2 of the Type Theory
podcast.

Git/LsTree.hs

@@ -44,7 +44,7 @@ lsTreeParams t = [ Params "ls-tree --full-tree -z -r --", File $ fromRef t ]
 lsTreeFiles :: Ref -> [FilePath] -> Repo -> IO [TreeItem]
 lsTreeFiles t fs repo = map parseLsTree <$> pipeNullSplitStrict ps repo
   where
-  	ps = [Params "ls-tree --full-tree -z --", File $ fromRef t] ++ map File fs
+	ps = [Params "ls-tree --full-tree -z --", File $ fromRef t] ++ map File fs
 
 {- Parses a line of ls-tree output.
  - (The --long format is not currently supported.) -}