net/http/httptest: fix incorrectly-named ResponseRecorder example
net/http/httptest: fix incorrectly-named ResponseRecorder example

R=golang-dev, minux.ma, r
CC=golang-dev
https://codereview.appspot.com/8545047

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