strconv: fix typo in docs
strconv: fix typo in docs

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/12709044

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

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