Fix directory structure for Haskell icon

As pointed out by @Thomas-Boi in [pull request 268](https://github.com/devicons/devicon/pull/268#issuecomment-684409627) the directory structure for the `Haskell` icon does not follow our guidelines. The error was made back in the [pull request 107](https://github.com/devicons/devicon/pull/107).

Also the Haskell icon is not added into the font yet.
