Docs: send-email: --chain_reply_to -> --[no-]chain-reply-to

Signed-off-by: Michael Witten <mfwitten@mit.edu>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Documentation/git-send-email.txt

@@ -221,7 +221,7 @@ sendemail.bcc::
 	Email address (or alias) to always bcc.
 
 sendemail.chainreplyto::
-	Boolean value specifying the default to the '--chain_reply_to'
+	Boolean value specifying the default to the '--[no-]chain-reply-to'
 	parameter.
 
 sendemail.smtpserver::