Revert "avoid modifying the current directory (haskell#326)"

This reverts commit 3e688d9.

This was causing test failures on the ghc9 upgrade

lsp/src/Language/LSP/Server/Processing.hs

@@ -87,6 +87,12 @@ initializeRequestHandler ServerDefinition{..} vfs sendFunc req = do
         rootDir = getFirst $ foldMap First [ params ^. LSP.rootUri  >>= uriToFilePath
                                            , params ^. LSP.rootPath <&> T.unpack ]
 
+    liftIO $ case rootDir of
+      Nothing -> return ()
+      Just dir -> do
+        debugM "lsp.initializeRequestHandler" $ "Setting current dir to project root:" ++ dir
+        unless (null dir) $ setCurrentDirectory dir
+
     let initialWfs = case params ^. LSP.workspaceFolders of
           Just (List xs) -> xs
           Nothing -> []
@@ -122,7 +128,7 @@ initializeRequestHandler ServerDefinition{..} vfs sendFunc req = do
   where
     makeResponseMessage rid result = ResponseMessage "2.0" (Just rid) (Right result)
     makeResponseError origId err = ResponseMessage "2.0" (Just origId) (Left err)
-
+    
     initializeErrorHandler :: (ResponseError -> IO ()) -> E.SomeException -> IO (Maybe a)
     initializeErrorHandler sendResp e = do
         sendResp $ ResponseError InternalError msg Nothing