docs(tutorial/7 - Routing): correct typos

[kchia]

I corrected several typos (e.g., missing commas) in the document. I believe these corrections would enhance readers' experience with the document.

[googlebot]

Thanks for your pull request.

It looks like this may be your first contribution to a Google open source project, in which case you'll need to sign a Contributor License Agreement (CLA) at https://cla.developers.google.com/.

If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check the information on your CLA or see this help article on setting the email on your git commits.

Once you've done that, please reply here to let us know. If you signed the CLA as a corporation, please let us know the company's name.

[kchia]

I just signed the CLA agreement.

Thank you,
Hou

[googlebot]

CLAs look good, thanks!