fix hit slop for bottom tab bar

[vonovak]

The problem this fixes is that if you currently tap just slightly above the tab bar, the button in the tab bar is going to respond to the tap - and it should not.

Two reasons for this change:

1. it breaks detox e2e test in the case when there is a tab navigator, and the screen in it has a scrollview that we're trying to scroll down ( await element(by.id('someScrollView')).scrollTo('bottom');)

The reason this doesn't work is that when detox tries to tap and drag the scrollView, detox taps just above the tab bar - within the reach of the hitslop - and instead of the scrollview responding, the scroll ends up being ignored.

2. if you take a look at a native app such as files, you'll see that taps outside the bounds of the tab bar are ignored. It should be the same for the tabs in react-navigation

[satya164]

Thanks for the PR