spec: Correct typo in method expressions example.
spec: Correct typo in method expressions example.

Also, remove unnecessary whitespace.

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/6928045

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang