crypto/elliptic: fix doc typo         Fixes issue 3735.
crypto/elliptic: fix doc typo
        Fixes issue 3735.

R=golang-dev, agl
CC=golang-dev
http://codereview.appspot.com/6301083

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