fix: render Common Extensions propertly in React 16 (#5930)

Avoid mapping Immutable.Map as React children.

Co-authored-by: Vladimir Gorej <vladimir.gorej@gmail.com>

Ref https://github.com/immutable-js/immutable-js/issues/667

src/core/plugins/oas3/components/request-body.jsx

@@ -150,7 +150,7 @@ const RequestBody = ({
                         <div className="parameter__type">
                           { type }
                           { format && <span className="prop-format">(${format})</span>}
-                          {!showCommonExtensions || !commonExt.size ? null : commonExt.map((v, key) => <ParameterExt key={`${key}-${v}`} xKey={key} xVal={v} />)}
+                          {!showCommonExtensions || !commonExt.size ? null : commonExt.entrySeq().map(([key, v]) => <ParameterExt key={`${key}-${v}`} xKey={key} xVal={v} />)}
                         </div>
                         <div className="parameter__deprecated">
                           { prop.get("deprecated") ? "deprecated": null }