Fixed props key was spread into JSX FitImage

[cc-matthias-m]

Hi,

With the last version of react-native (0.75.4), the package display a warning for a deprecated code :

 ERROR  Warning: A props object containing a "key" prop is being spread into JSX:
  let props = {key: someKey, indicator: ..., style: ..., source: ..., accessible: ..., accessibilityLabel: ...};
  <FitImage {...props} />
React keys must be passed directly to JSX without using spread:
  let props = {indicator: ..., style: ..., source: ..., accessible: ..., accessibilityLabel: ...};
  <FitImage key={someKey} {...props} />

So I create this PR to fix it. As you can see, it’s really a light commit.

This PR work with last react-native version and previous one.

Do you think create a new npm patch 7.0.3 to add this modification ?

Thanks for reading.