Documentation: use lowercase for shallow and deep threading

Even when a sentence is started with 'shallow' or 'deep' use the
lowercase version to maintain consistency.

Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -745,11 +745,11 @@ format.pretty::
 
 format.thread::
 	The default threading style for 'git-format-patch'.  Can be
-	either a boolean value, `shallow` or `deep`.  'Shallow'
+	either a boolean value, `shallow` or `deep`.  `shallow`
 	threading makes every mail a reply to the head of the series,
 	where the head is chosen from the cover letter, the
 	`\--in-reply-to`, and the first patch mail, in this order.
-	'Deep' threading makes every mail a reply to the previous one.
+	`deep` threading makes every mail a reply to the previous one.
 	A true boolean value is the same as `shallow`, and a false
 	value disables threading.
 

Documentation/git-format-patch.txt

@@ -128,9 +128,9 @@ include::diff-options.txt[]
 	the Message-Id header to reference.
 +
 The optional <style> argument can be either `shallow` or `deep`.
-'Shallow' threading makes every mail a reply to the head of the
+'shallow' threading makes every mail a reply to the head of the
 series, where the head is chosen from the cover letter, the
-`\--in-reply-to`, and the first patch mail, in this order.  'Deep'
+`\--in-reply-to`, and the first patch mail, in this order.  'deep'
 threading makes every mail a reply to the previous one.  If not
 specified, defaults to the 'format.thread' configuration, or `shallow`
 if that is not set.