Fix progress bar

[ferrannp]

We broke it. It shows an indeterminate circle right now.

[lukewalczak]

@satya164 @ferrannp probably we have to wait for fix this issue within react native. Read the discussion in the commit

[ferrannp]

We need to update react-native. I checked that in 0.50.3 the progress bar is ok again.

[lukewalczak]

Thanks to Satya's PR #208 it works properly again! 🎊