Write Yaml string to File
@param {string} file - File path
@param {object} data - Object to turn into Yaml
@param {function} cb - Optional callback when done
@see writeYamlFileSync
function writeYamlFile(file, data, cb) {
  fs.writeFile(file, yaml.safeDump(data), () => {
    if (cb) cb();
  });
}