cmap_keys.8: Fix spelling and grammar errors

• "There are informations" changed to "There is information"
• Other occurrences of informations changed to information

Original patch was created by Richard B Winters <rik@mmogp.com>, so
thanks for it.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Steven Dake <sdake@redhat.com>