[Translation] Update PluralizationRules.php

As a native brazilian portuguese speaker, and also respecting http://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html#pt definitions, 0 elements are normally used in plural form.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT