fix typo

Actually the reader accepts (list 'a'b) = (list 'a 'b); it still looks
wrong.
bind-keys: ,@(when map (list map)) => map

Omitting map is same as passing nil.
bind-keys: bind directly to prefix-map

instead of constructing equivalent key sequence by string concatenation.
This allows specifying vector key sequences, as in bind-key (since
aed85970814b6a3efd4c86f84041bf3214a8fc82).