Roll back unnecessary dependency updates

[foggy1]

Since merging the new dependencies, there are a couple of critical issues (#37 & #39) that I don't get when running off of my fork. I think it would be prudent to only upgrade what's absolutely necessary to get this to run on react-native 0.50 and above rather than introducing multiple dependency changes, especially since the tests for this library aren't representative of whether it functions right now.

The fork I'm merging works in a production app and covers the bare minimum case. It also has issue #40 but that's nothing but a console warning, and tests/type-checking for this lib should be upgraded separately anyway.

(All those having the aforementioned critical issues are again encouraged to use my fork https://github.com/foggy1/react-native-snackbar-dialog/archive/upgrade-flow-type-babel.tar.gz as a dependency and place cd node_modules/react-native-snackbar-dialog && yarn build in your postinstall script.)

[iRoachie]

Any reason why this isn't merged? No one can use this library at all because of this error.