WP15: Incorrect link in notice to translators

[pedromendonca]

For the Portuguese (pt_PT) version of the WP15 site, the call to translators to help completing the translation has an incorrect link.

The call to action is currently hidden as the translation is complete, but will surely apear again as soon as there are new strings to translate.

Current wrong link:
​https://translate.wordpress.org/projects/meta/wp15/pt-pt/default

It should link to:
​https://translate.wordpress.org/projects/meta/wp15/pt/default

[pedromendonca]

Notice for translators

[coreymckrill]

In 7080:

WP15 locales: Use the correct locale string in the contribute URL

Fixes #3561

[coreymckrill]

Thanks for the report, @pedromendonca !