Fix casing of HTML attributes

[utkarshkukreti]

React uses camel case versions for several HTML attributes, e.g. readonly -> readOnly. The current values were copied from bs-preact; they work with Preact but React prints a warning if they're used.

Possibly complete list: https://github.com/facebook/react/blob/40568e9773276d94e6aa5b70fed4355a7291827f/packages/react-dom/src/shared/possibleStandardNames.js.