fix androidX legacy dependencies...

[diegojimenes]

this is a hacky way to detect when to use the legacy dependecies
from androidX.

let me know if there is a better way.

[diegojimenes]

also, people might need to run this command npx jetify && npx react-native run-android.

[congnguyen91]

I think this PR should be checked :) @tolu360 now React Native 0.60 has released & supported Android-X. A few of modules upgraded. There are two options:

1. Only support android-x for the next version (if the current version was stable).
2. Support both of non-android-x & android-x config.

[diegojimenes]

Yes, @congnguyen91. This should keep compatibility with both, for now.
Maybe later, we can drop the support for non-androidX.

[tolu360]

Hi guys! I would take a look at this PR, thanks @diegojimenes! I do prefer we keep support for both for the nearest future - I may release androidX support on a beta for now. I haven't even played with 0.60.* myself, but would surely make out time.