Corrects spelling error in README.md

optomized -> optimized
Merge pull request #67 from KevinTCoughlin/patch-1

Corrects "optomized" spelling error in README.md
Resolve default locale from `Intl`

This improves how the default locale is determined by resolving it from an `Intl.NumberFormat` instance. This change still allows for the developer to explicitly set `IntlMessageFormat.defaultLocale` if they wish.

This change was a continuation of #66
Build
1.0.0-rc-3