doc: fix typo in sendemail.identity

Saying "the this" is an obvious typo. But while we're here,
let's polish the English on the second half of the sentence,
too.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -2797,8 +2797,8 @@ sendemail.smtpsslcertpath::
 
 sendemail.<identity>.*::
 	Identity-specific versions of the 'sendemail.*' parameters
-	found below, taking precedence over those when the this
-	identity is selected, through command-line or
+	found below, taking precedence over those when this
+	identity is selected, through either the command-line or
 	`sendemail.identity`.
 
 sendemail.aliasesFile::