Fix typo: <Pulg> -> <Plug>

Just noticed this while scanning the code.

BTW, so as to not clutter the issues / mailing list, you are creating
buffer-local mappings guarded by `if hasmapto` clauses:

```vim
  if !hasmapto("<Plug>clj_repl_eval.", "i")
    imap <buffer> <silent> <C-e> <Plug>clj_repl_eval.
  endif
```

However, if there is no event associated with redl#repl#create(), how
can users provide their own mappings to <Plug>clj_repl_* without mapping
them globally in the clojure FileType?

Great work!

    guns