Fix phone error

Author: PaitoAnderson

pages/checkout/index.js

@@ -369,7 +369,7 @@ class CheckoutPage extends Component {
  firstname: this.state['customer[first_name]'],
  lastname: this.state['customer[last_name]'],
  email: this.state['customer[email]'],
- phone: this.state['customer[phone]']
+ phone: this.state['customer[phone]'] || undefined
  },
  // collected 'order notes' data for extra field configured in the Chec Dashboard
  extrafields: {