Fix self-closing tag to match with react-i18next

[yoo2001818]

Why am I submitting this PR

This PR corrects the behavior of <br /> to match with react-i18next's nodeToString routine.

When transSupportBasicHtmlNodes is true, inside <Trans>, react-i18next converts <br /> into <br/>. But i18next-parser converts <br /> into <br />, causing a difference between the defaultValue generated with each other.

If i18nKey is specified, this wouldn't cause any problem because only defaultValue would differ, and both <br/> and <br /> can be parsed well by react-i18next.

However, if only defaultValue is specified, the defaultValue will be used as the i18nKey. Therefore it makes generated key and the actual key to mismatch, making react-i18next unable to find the translation entry.

Does it fix an existing ticket?

No

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• tests are included and pass: yarn test (see details here)
• documentation is changed or added

FYI) I've encountered a failing test while running tests. I investigated the problem, and it turned out that Intl.PluralRules defaults to the system language if an unknown locale is specified - so the test will fail if the system language is set to other languages that have more/less than 2 plural types.

(Intl.PluralRules is used by i18next.PluralResolver.)

The test can be successfully run by changing the system language to en-US:

LANG='en-US' yarn test

  1) parser
       options
         generates one plural key for unknow languages:

      Uncaught AssertionError: expected { 'test {{count}}_other': '' } to deeply equal { 'test {{count}}_one': '', …(1) }
      + expected - actual

       {
      +  "test {{count}}_one": ""
         "test {{count}}_other": ""
       }