complete(data, done) {
    if (data.last !== 'yo' && !data.last.startsWith('-')) {
      return this.generator(data, done);
    }

    this.env.lookup().then(() => {
      const meta = this.env.getGeneratorsMeta();
      const results = Object.keys(meta).map(this.item('yo'), this);
      done(null, results);
    }, done);
  }
Completion event done

@param {String}   data   Environment object as parsed by tabtab
@param {Function} done   Callback to invoke with completion results