      doc: fix typo in Concurrency Patterns article
      doc: fix typo in Concurrency Patterns article

Fixes issue 3178.

R=golang-dev, iant
CC=golang-dev
http://codereview.appspot.com/6506064

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