Update dependency i18next to v15

Thalia Technicie
2019-05-30T11:16:31+02:00

This MR contains the following updates: | Package | Type | Update | Change | References | |---|---|---|---|---| | i18next | dependencies | major | [`14.1.1` -> `15.1.3`](https://diff.intrinsic.com/i18next/14.1.1/15.1.3) | [homepage](htt...

i18next | dependencies | major | 14.1.1 -> 15.1.3 | homepage, source