Update tools.md

tools.md

@@ -18,7 +18,12 @@ It's a bit fragile, more than a bit slow, and it's not worth the grief.
 
 - Vim
   - We recommend [Stephen Diehl's vim instructions](http://www.stephendiehl.com/posts/vim_2016.html) but we suggest replacing ghc-mod with the below for now.
-  - For getting type errors in vim reliably (in lieu of ghc-mod):  https://github.com/ishiy1993/dotfiles/blob/master/.vimrc#L176-L177
+  - For getting type errors in vim reliably (in lieu of ghc-mod)
+    ```
+    autocmd FileType haskell setlocal makeprg=stack\ build
+    autocmd FileType haskell setlocal errorformat=%f:%l:%v:%m
+    ```
+    from: https://github.com/ishiy1993/dotfiles/blob/master/.vimrc
 
 - [Sublime Text](https://github.com/SublimeHaskell/SublimeHaskell)