doc/gitremote-helpers: fix missing single-quote

The formatting around "option push-option" was missing its closing
quote, leading to the output having a stray opening quote, rather than
rendering the item in italics (as we do for all of the other options in
the list).

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

Documentation/gitremote-helpers.txt

@@ -517,7 +517,7 @@ set by Git if the remote helper has the 'option' capability.
 'option pushcert' {'true'|'false'}::
 	GPG sign pushes.
 
-'option push-option <string>::
+'option push-option' <string>::
 	Transmit <string> as a push option. As the push option
 	must not contain LF or NUL characters, the string is not encoded.