Fix repl for Node 0.11.12.

Node changed their repl so that it inherits from readline.Interface.
This means that `prompt` is now the rli function and not the original
prompt string.  This may be a little hacky, but I figure it would give
someone a start if they want to do a better fix.

The commit that changed this in Node is joyent/node@3ae0b17c76f693dd2e68a46f78c7dc7f595b33c6

This bug was mentioned in Issue #3395.