message: only unshift default if there is no deviceId===default
diff: @@ -958,7 +958,9 @@ module.exports = React.createClass({
  const audioInputs = this.state.mediaDevices.audioinput;
  if (audioInputs.length > 0) {
  + if (!audioInputs.some((input) => input.deviceId === 'default')) {
  audioInputs.unshift(defaultOption);
  + }
  microphoneDropdown = <div>
  <h4>Microphone</h4>
  <Dropdown
  @@ -972,7 +974,9 @@ module.exports = React.createClass({
  const videoInputs = this.state.mediaDevices.videoinput;
  if (videoInputs.length > 0) {
  + if (!videoInputs.some((input) => input.deviceId === 'default')) {
  videoInputs.unshift(defaultOption);
  + }
  webcamDropdown = <div>
  <h4>Cameras</h4>
  <Dropdown
  