title: CycleJS makeHTTPDriver _add is not a function
body: <p>Just getting started with CycleJs and I've hit a wall with this error. </p>
  
  <p>Basically, I'm running the <a href="https://github.com/cyclejs/cyclejs/tree/master/examples/isomorphic" rel="nofollow noreferrer">isomorphic example</a>
  and adding on HTTP Driver so I can send requests</p>
  
  <p>server.js</p>
  
  <pre><code>function wrapAppResultWithBoilerplate(appFn, context$, bundle$) {
    return function wrappedAppFn(sources) {
      const vdom$ = appFn(sources).DOM;
      const wrappedVDOM$ = xs
        .combine(vdom$, context$, bundle$.take(1))
        .map(wrapVTreeWithHTMLBoilerplate)
        .last();
      return Object.assign({}, sources, { DOM: wrappedVDOM$ });
    };
  }
  ...
  const context$ = xs.of({ route: req.url });
  const wrappedAppFn = wrapAppResultWithBoilerplate(
    app,
    context$,
    clientBundle$
  );
  run(wrappedAppFn, {
    DOM: makeHTMLDriver(html =&gt; res.send(prependHTML5Doctype(html))),
    context: () =&gt; context$,
    PreventDefault: () =&gt; {},
    HTTP: makeHTTPDriver()
  });
  ...
  </code></pre>
  
  <p>Stacktrace</p>
  
  <pre><code>TypeError: (intermediate value)(intermediate value)._add is not a function
  at MapFlatten._n (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:954:35)
  at Stream._n (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1193:22)
  at CombineListener._n (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:345:30)
  at MemoryStream.Stream._n (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1193:22)
  at MemoryStream._n (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:2110:13)
  at StartWith._start (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1112:14)
  at MemoryStream._add (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:2128:23)
  at Combine._start (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:396:14)
  at Stream._add (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1250:23)
  at MapFlatten._start (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:928:20)
  at Stream._add (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1250:23)
  at Combine._start (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:396:14)
  at Stream._add (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1250:23)
  at MapOp._start (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:983:14)
  at Stream._add (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1250:23)
  at Last._start (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:851:14)
  at Stream._add (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1250:23)
  at Stream.addListener (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1310:10)
  at Stream.subscribe (/Users/jethrolarson/github/isomorphic/node_modules/xstream/src/index.ts:1330:10)
  at /Users/jethrolarson/github/isomorphic/node_modules/@cycle/run/src/index.ts:143:54
  at Array.map (native)
  at replicateMany (/Users/jethrolarson/github/isomorphic/node_modules/@cycle/run/src/index.ts:143:6)
  at run (/Users/jethrolarson/github/isomorphic/node_modules/@cycle/run/src/index.ts:230:32)
  at run (/Users/jethrolarson/github/isomorphic/node_modules/@cycle/run/src/index.ts:272:10)
  at /Users/jethrolarson/github/isomorphic/server.js:105:5
  at Layer.handle [as handle_request] (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/layer.js:95:5)
  at trim_prefix (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:317:13)
  at /Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:284:7
  at Function.process_params (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:335:12)
  at next (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:275:10)
  at expressInit (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/middleware/init.js:40:5)
  at Layer.handle [as handle_request] (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/layer.js:95:5)
  at trim_prefix (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:317:13)
  at /Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:284:7
  at Function.process_params (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:335:12)
  at next (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:275:10)
  at query (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/middleware/query.js:44:5)
  at Layer.handle [as handle_request] (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/layer.js:95:5)
  at trim_prefix (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:317:13)
  at /Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:284:7
  at Function.process_params (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:335:12)
  at next (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:275:10)
  at Function.handle (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/router/index.js:174:3)
  at EventEmitter.handle (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/application.js:174:10)
  at Server.app (/Users/jethrolarson/github/isomorphic/node_modules/express/lib/express.js:38:9)
  at emitTwo (events.js:106:13)
  at Server.emit (events.js:191:7)
  at HTTPParser.parserOnIncoming [as onIncoming] (_http_server.js:543:12)
  at HTTPParser.parserOnHeadersComplete (_http_common.js:105:23)
  </code></pre>