Preforming some async operations with Rx.js

I tried to come up with a good challenge to learn some Rx.js programming and I came up with this chain of operations below. As well as a bit of code that works and does these things.

1. Take github username
2. Create folder based on username (/repos-${user})
3. Get all repos for username (https://api.github.com/users/${user}/repos)
4. Get the hash of the repo data
5. Create file where name is hash and content is repo

I'm looking for insights and optimizations, shortcuts, etc, to make this better.

Here's the code.

import { join } from 'path'
import axios from 'axios'
import Rx from 'rx'
import Promise from 'bluebird'
import crypto from 'crypto'
import fs from 'fs-extra'
import Debug from 'debug'

let debug = Debug('github-repos')

Promise.promisifyAll(fs)

let {
  ensureDirAsync,
  outputJsonAsync } = fs

function getRepos (user) {
  let theUrl = `https://api.github.com/users/${user}/repos`
  return axios.get(theUrl)
  .then(result => {
    debug(`got results back for ${user}`)
    return result.data
  })
}

function getHash (json) {
  let text = JSON.stringify(json)
  return crypto.createHash('md5').update(text).digest('hex')
}

function createDir (user) {
  return ensureDirAsync(join(__dirname, `/repos-${user}`))
}

function createFile (user, hash, data) {
  let file = join(__dirname, `/repos-${user}/${hash}.json`)
  return outputJsonAsync(file, data).then(x => file)
}

let ghUser$ = Rx.Observable.from(['reggi', 'jackofseattle', 'nolanlawson'])

let ensureUser$ = ghUser$
  .do((u) => debug(`Creating directory for: ${u}`))
  .flatMap(u => createDir(u))

let getRepos$ = ghUser$
  .do((u) => debug(`fetching user repos for: ${u}`))
  .flatMap(u => getRepos(u))

let repos$ = getRepos$
  .flatMap(repos => repos.map(repo => ({hash: getHash(repo), repo})))  // create hash for each

let fileWriter$ = repos$
  .map(repo => ({user: repo.repo.owner.login, hash: repo.hash, repo: repo.repo}))
  .flatMap(({user, hash, repo}) => {
    return createFile(user, hash, repo)
  })
  .do((file) => debug(`wrote a new repo to json ${file}`))
  .toArray()

let reposSubscription = fileWriter$.subscribe(
  function (x) {
    debug('subscription')
  },
  function (err) {
     console.log('Error: %s', err)
  },
  function (e) {
     debug('Completed')
  });