Fix base tag subfolder example

[jerolba]

The sample url for production server is "http://www.mysite.com/mysrc/app/"
but the identified subfolder is "my/app", which doesn't match.

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[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

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• 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 your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[jerolba]

I signed it!

[googlebot]

CLAs look good, thanks!

[googlebot]

CLAs look good, thanks!

[filipesilva]

LGTM, thanks for the fix!