[FIX] - In Viewpager, Flatlist's key needs to be a string

[dpnolte]

Warning is displayed in react native 0.60.3:

Warning: Failed child context type: Invalid child context virtualizedCell.cellKey of type number supplied to CellRenderer, expected string.

The warning is removed when replacing the key from a number to a string

[azmifareed]

Can this be merged in please?

[GitHubGreg]

Thanks for the outstanding tool, excellent.

I've also been getting this warning, would be great if this fix could be merged.