code: function resolveConfig (fileName, options) {
    options = options || {}
    var schema = options.schema
    var resolvePackageJson = options.resolvePackageJson || false
    var fileNames = [fileName, resolvePackageJson ? 'package.json' : null].filter(
      item => !!item
    )
    const results = upResolve(fileNames)
    return Promise.all(results.map(readFileAsync))
      .then(parseFiles(options))
      .then(validateSchema(schema))
      .then(reduceConfigs)
  }
docs: Resolves config files, parses and combines them with priority to the nearest file
  @param {String} fileName
  @param {Object} options
  @param {Object} options.schema - validation options, see https://www.npmjs.com/package/jsonschema
  @param {boolean} options.resolvePackageJson - also include config from package.json
  @param {String} options.packageJsonKey - key to extract config from package json. eg {version: "0.0.1", deps: {...}, myConfg: {...}} => myConfig