config.txt: fix a typo (backslash != backquote)

Signed-off-by: Štěpán Němec <stepnem@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -63,7 +63,7 @@ The variable names are case-insensitive, allow only alphanumeric characters
 and `-`, and must start with an alphabetic character.
 
 A line that defines a value can be continued to the next line by
-ending it with a `\`; the backquote and the end-of-line are
+ending it with a `\`; the backslash and the end-of-line are
 stripped.  Leading whitespaces after 'name =', the remainder of the
 line after the first comment character '#' or ';', and trailing
 whitespaces of the line are discarded unless they are enclosed in