Attach Lo-Dash as n_ to the REPL context

The `_` character is special in the Node REPL. See http://nodejs.org/api/repl.html#repl_repl_features

So that means after doing something like > 1 + 2, which will produce 3, the value of _ is 3

See https://github.com/joyent/node/blobb5175003bca45e23bd20d9559096dafda3e0ad7c/lib/repl.js#L318

Fixed the issue by attaching Lo-Dash as n_ to the REPL context.

References:

    Closes https://github.com/borisdiakur/n_/issues/1