fix(prop-types): check for react components via PropTypes.elementType (#4025)

packages/netlify-cms-widget-list/src/ListControl.js

@@ -101,7 +101,7 @@ export default class ListControl extends React.Component {
     classNameWrapper: PropTypes.string.isRequired,
     setActiveStyle: PropTypes.func.isRequired,
     setInactiveStyle: PropTypes.func.isRequired,
-    editorControl: PropTypes.func.isRequired,
+    editorControl: PropTypes.elementType.isRequired,
     resolveWidget: PropTypes.func.isRequired,
     clearFieldErrors: PropTypes.func.isRequired,
     fieldsErrors: ImmutablePropTypes.map.isRequired,