Added .stack-work/ directory to Haskell .gitignore.
.stack-work/ is a work directory used by the `stack` build tool.
The `stack` build tool has recently been gaining a lot of traction in
the Haskell community. It is very similar to the `cabal` build tool,
which also has entries in this Haskell .gitignore file.
(cdep) illabout