This is a deliberate limitation across all sites, to avoid trivial edits. In your case the limitation is definitely annoying, since that 1-character edit is decidedly not trivial. You can raise this issue on SO meta, but in general, the accepted work-around is to just add a few more actually-trivial edits into your edit. Fix spaces, punctuation, whatever little things you can find.
If you can't find anything, you can always add "invisible" information, such as an XML comment: the text <!-- edited for character count --> will not be seen.
Also note that the Edit Questions and Answers privilege, unlocked at 2,000 reputation, removes the character edit limitation.
