silentFallbackWarn does not apply to datetime localization #558

vue & vue-i18n version

vue: 2.6.10
vue-i18n: 8.8.2

Reproduction Link

Steps to reproduce

1. Set datetimeFormats and silentFallbackWarn when initialize VueI18n
2. Use $d in a child component

What is Expected?

When the datetime format is available in root component, there should be no warning in console.

What is actually happening?

There are still warnings in console.