fix: <Trans /> warns 'Each child in a list should have a unique "key" prop.'

[aiktb]

close #1805

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• run tests npm run test
• tests are included
• commit message and code follows the Developer's Certification of Origin

Checklist (for documentation change)

• only relevant documentation part is changed (make a diff before you submit the PR)
• motivation/reason is provided
• commit message and code follows the Developer's Certification of Origin

[coveralls]

coverage: 97.079% (+0.002%) from 97.077%
when pulling dff7130 on aiktb:master
into 9569f9f on i18next:master.

[adrai]

thank you... it's included in v15.1.0