clarify fn() in first level of prec

Reference: /n/atom/patch/applied2013/precclear
Date: Sun Jun 23 18:06:15 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /rc/bin/prec	Sun Jun 23 18:05:57 2013
+++ /rc/bin/prec	Sun Jun 23 18:05:57 2013
@@ -1,7 +1,7 @@
 #! /bin/rc
 label prec
 cat <<!
-left to right	fn() [] -> .
+left to right	() [] -> .
 right to left	! ~ ++ -- - (type) * & sizeof
 left to right	* / %
 left to right	+ -