Fix typo in the instructions

Hi Jason,

After 8 long years free from bug-reports, it seems I've discovered the sole, almost insignificant flaw in this simple but great Vim plugin. :)

As a fan of typographically correct punctuation, I've been happily using UniCycle (great name, BTW) since I discovered it a month ago - much more convenient than having to check the docs to find out the correct digraph.

Regards,
Anthony