Fix retrocompat with React 16 and TypeScript 3 https://github.com/garronej/tss-react/issues/95

src/lib/i18n/index.tsx

@@ -1,5 +1,6 @@
 import "minimal-polyfills/Object.fromEntries";
 //NOTE for later: https://github.com/remarkjs/react-markdown/blob/236182ecf30bd89c1e5a7652acaf8d0bf81e6170/src/renderers.js#L7-L35
+import React from "react";
 import ReactMarkdown from "react-markdown";
 import memoize from "memoizee";
 import { kcMessages as kcMessagesBase } from "./generated_kcMessages/18.0.1/login";