fix incorrect escape of "\".

Reference: /n/atom/patch/applied2013/runeclassnit
Date: Thu Jun 13 15:35:33 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/man/2/runeclass	Thu Jun 13 15:35:07 2013
+++ /sys/man/2/runeclass	Thu Jun 13 15:35:07 2013
@@ -25,7 +25,7 @@
 For example
 .IP
 .EX
-	echo e\u0308 | rune/uconv | rune/compose
+	echo e\\u0308 | rune/uconv | rune/compose
 .EE
 .SH "SEE ALSO
 .IR grep (1) ,