why I can't combine streams using xstream in cyclejs?

I'm being trying unsuccesfully to combine to streams into one, and show the text in a h1.

But not being able to make it work:

this is my code:

function main(sources) {
  // single streams
  let letter$ = xs.of({text: 'abcd'}); 
  let number$ = xs.of({text: '123456'});

  //try to combine them into one
  const combined$ = 
    xs.combine( letter$, number$ ).
      map( ( [ letter, number ] ) => {
        return { text: letter.text + ' ' + number.text };
      });

  //updates the virtual dom with the reponse
  const vdom$ = combined$
    .map(o => o.text) 
    .startWith('Loading...')
    .map(text =>
      div('.container', [
        h1(text)
      ])
    );


  return {
    DOM: vdom$
  };
}

It shows error saying:

index.js:6 TypeError: f is not a function
at invoke (core.js:36)
at CombineListener._n (core.js:72)
at Stream._n (core.js:886)
at FromArrayProducer._start (core.js:142)
at Stream._add (core.js:959)
at CombineProducer._start (core.js:118)
at Stream._add (core.js:959)
at MapOperator._start (core.js:681)
at Stream._add (core.js:959)
at StartWithOperator._start (core.js:786)

being trying to understand why but no luck so far.

My problem was using the dependencies specified in the package.json of the examples in the CycleJS repo.

Those dependencies are outdated:

https://github.com/cyclejs/cyclejs/blob/master/examples/http-search-github/package.json

"dependencies": {
   "@cycle/xstream-run": "1.1.0",
   "@cycle/dom": "10.0.0-rc20",
   "@cycle/http": "9.0.0-rc3",
   "xstream": "2.4.x"
}

and the dependencies to date are:

"@cycle/dom": "^12.1.0",
"@cycle/http": "^10.1.0",
"@cycle/xstream-run": "^3.0.4",
"xstream": "^5.3.6"

rule of thumb check for the latest stable dependencies.

thanks @bloodyKnuckles, and everybody in the CycleJS gitter.