[x/tour] content: fix typo in flowcontrol/2
[x/tour] content: fix typo in flowcontrol/2

Fixes golang/tour#575

Change-Id: Ic86fcddbd72b6a54e75b794b0b760151e2a4b78c
Reviewed-on: https://go-review.googlesource.com/128536
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
X-Tour-Commit: d642b9371986f5bb2152547a0d525a57f634c3ef

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website