Fix "key" prop warning

[mlazari]

When using version 18.3.0 of "react" there is a warning saying that react keys must be passed directly to JSX without using spread (added in facebook/react#25697):

 ERROR  Warning: A props object containing a "key" prop is being spread into JSX:
  let props = {key: someKey, postprocessValue: ..., hideRoot: ..., shouldExpandNode: ..., collectionLimit: ..., sortObjectKeys: ..., getItemString: ..., keyPath: ..., labelRenderer: ..., nodeType: ..., styling: ..., value: ..., valueRenderer: ..., data: ..., isCustomNode: ...};
  <JSONObjectNode {...props} />
React keys must be passed directly to JSX without using spread:
  let props = {postprocessValue: ..., hideRoot: ..., shouldExpandNode: ..., collectionLimit: ..., sortObjectKeys: ..., getItemString: ..., keyPath: ..., labelRenderer: ..., nodeType: ..., styling: ..., value: ..., valueRenderer: ..., data: ..., isCustomNode: ...};
  <JSONObjectNode key={someKey} {...props} />
    in JSONNode (created by JSONTree)

[Dean177]

Thanks!