Super mod: update Travis Firefox version

travis-firefix.js

var fs = require('fs')
var path = require('path')

module.exports = {
  getOptions: function () {
    return [{
      name: 'version',
      type: 'input',
      default: '51.0',
      message: 'New Firefox version:'
    }]
  },
  
  run: function (directory, options) {
    var version = options.version
    version = version.trim()
    var filepath = path.join(directory, '.travis.yml')
    if (!fs.existsSync(filepath)) {
      console.error('"' + filepath + '" was not found, cannot update Firefox version')
      return Promise.resolve()
    }
    
    return new Promise(function (resolve, reject) {
      fs.readFile(filepath, {encoding: 'utf8'}, function (error, text) {
        error ? reject(error) : resolve(text)
      })
    }).then(function (text) {
      var newFirefox = 'firefox: "' + version + '"'
      var newText = text.replace(/firefox: "(.*)"/, newFirefox)
      if (newText === text) {
        console.error('Firefox version not previously specified, unable to update.')
      }
      return newText
    }).then(function (newText) {
      return new Promise(function (resolve, reject) {
        fs.writeFile(filepath, newText, function (error) {
          error ? reject(error) : resolve()
        })
      })
    })
  }
}