message: example code - explain why we need XHR standin, even though
  we are using a "direct" RPC config
diff: @@ -37,7 +37,8 @@ function setUpTest() {
  describe("RobotWorldRpc", () => {
  - // install mock of browser's XMLHttpRequest for unit tests
  + // This node-based implementation of XHR is *not* required by our RPC mechanism. It is required by our
  + // I18n module (specifically the i18next package).
  (global as any).XMLHttpRequest = require("xmlhttprequest").XMLHttpRequest; // tslint:disable-line:no-var-requires
  it("should run robotworld through RPC as a client", async () => {
  