AndroidX migration required

[mortenholmgaard]

Please migrate to AndroidX if this libary should continue to be usable, as this is a requirement for Google Play as of 1. of november do to min api 28 and firebase for that version requires AndroidX.

[veghtomi]

@mortenholmgaard AndroidX is not yet necessary. What is necessary is to update targetSdk to api 28. I have created a pull request and after review, it will be merged and released. #84