Make VuiFormGroup play nicely with VuiTextArea

[cjcenizal]

Currently, placing a VuiTextArea inside a VuiFormGroup yields this error in the browser console:

react-dom.development.js:67 Warning: React does not recognize the `isInvalid` prop on a DOM element. If you intentionally want it to appear in the DOM as a custom attribute, spell it as lowercase `isinvalid` instead. If you accidentally passed it from a parent component, remove it from the DOM element.
    at textarea
    at http://127.0.0.1:8080/script.js:40628:8
    at VuiFormGroup (http://127.0.0.1:8080/script.js:41557:25)

Repro case:

      <VuiFormGroup label="Summary prompt name" labelFor="summaryPromptName">
        <VuiTextInput value={summaryPromptName} onChange={(e) => onUpdateSummaryPromptName(e.target.value)} fullWidth />
      </VuiFormGroup>