date-formats.txt: Typo fix

Last time I checked, I was living in the UTC+01:00 time zone. UTC+02:00
would be Central European _Summer_ Time.

Signed-off-by: Luis Ressel <aranea@aixah.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/date-formats.txt

@@ -11,7 +11,7 @@ Git internal format::
 	It is `<unix timestamp> <time zone offset>`, where `<unix
 	timestamp>` is the number of seconds since the UNIX epoch.
 	`<time zone offset>` is a positive or negative offset from UTC.
-	For example CET (which is 2 hours ahead UTC) is `+0200`.
+	For example CET (which is 1 hour ahead of UTC) is `+0100`.
 
 RFC 2822::
 	The standard email format as described by RFC 2822, for example