regexp: doc fix
regexp: doc fix

This must have been from when "error" was a good variable
name for an "os.Error". But we use "err" these days.

R=golang-dev, dsymonds, r
CC=golang-dev
https://codereview.appspot.com/9132045

pombredanne/go-deleteme,tv42/old-go,tv42/old-go,dsriram/golang,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,apparentlymart/golang,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,dsriram/golang,tv42/old-go,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,gnanderson/go,apparentlymart/golang,dsriram/golang,gnanderson/go,apparentlymart/golang,dsriram/golang,apparentlymart/golang