Runtime error if options are array of strings

If options are array of strings:

			<Select
				options={["a", "b", "c"]}
				value={value}
				getOptionValue={e => e}
				getOptionLabel={e => e}
				onChange={e => setValue(e)}
			/>

There is a runtime error:

Uncaught TypeError: Cannot use 'in' operator to search for 'options' in 1

Which happens here: https://github.com/JedWatson/react-select/blob/master/packages/react-select/src/Select.tsx#L382

Sometimes it is really convenient if options is an array of predefined strings (enum).

It could be fixed just by doing a typeof guard.

Start in packages/react-select/src/Select.tsx around line 382 and reproduce the issue with the provided Select example using string options. Trace the failing runtime path and verify the fix against string options with getOptionValue and getOptionLabel callbacks; done means the example no longer throws the reported TypeError.