added dep for custom-setup

stack build failed w/o this though cabal old-build succeeded.

git-annex.cabal

@@ -296,6 +296,7 @@ source-repository head
 custom-setup
   Setup-Depends: base (>= 4.11.1.0), hslogger, split, unix-compat, process,
     filepath, exceptions, bytestring, directory, IfElse, data-default,
+    filepath-bytestring (>= 1.4.2.1.1),
     utf8-string, transformers, Cabal
 
 Executable git-annex