Babel 6 async error

.babelrc

{
  "presets": ["es2015", "stage-0"]
}

abc.js

export default class Abc {
  async test() {
    let client;

    return await this.timeout()
  }

  timeout() {
    return new Promise((resolve, reject) => {
      setTimeout(resolve, 1000)
    });
  }
}

gistfile1.txt

ReferenceError: client is not defined
    at Abc._callee2$ (abc.js:3:15)
    at tryCatch (/Users/baonguyen/Projects/sandbox/async-test/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/regenerator/runtime.js:62:40)
    at GeneratorFunctionPrototype.invoke [as _invoke] (/Users/baonguyen/Projects/sandbox/async-test/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/regenerator/runtime.js:338:22)
    at GeneratorFunctionPrototype.prototype.(anonymous function) [as next] (/Users/baonguyen/Projects/sandbox/async-test/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/regenerator/runtime.js:95:21)
    at step (/Users/baonguyen/Projects/sandbox/async-test/abc.js:9:273)
    at /Users/baonguyen/Projects/sandbox/async-test/abc.js:9:443
    at new Promise (/Users/baonguyen/Projects/sandbox/async-test/node_modules/babel-cli/node_modules/babel-polyfill/node_modules/core-js/modules/es6.promise.js:197:7)
    at /Users/baonguyen/Projects/sandbox/async-test/abc.js:9:99
    at Abc.test (abc.js:5:32)
    at _callee$ (main.js:7:15)

main.js

import Abc from './abc.js'

let abc = new Abc();

async function main() {
  try {
    await abc.test()
  }
  catch (ex) {
    console.log(ex.stack)
  }
}

main()