Use HTMLMediaObject.srcObject in webcam-transfer-learning video stream. (#52)

Fix a deprecation warnings about using the HTMLMediaElement.srcObject instead of URL.createObjectURL api.

> [Deprecation] URL.createObjectURL with media streams is deprecated and will be removed in M68, around July 2018. Please use HTMLMediaElement.srcObject instead. See https://www.chromestatus.com/features/5618491470118912 for more details.

Author: fraserxu

webcam-transfer-learning/webcam.js

@@ -87,7 +87,7 @@ export class Webcam {
         navigator.getUserMedia(
             {video: true},
             stream => {
-              this.webcamElement.src = window.URL.createObjectURL(stream);
+              this.webcamElement.srcObject = stream;
               this.webcamElement.addEventListener('loadeddata', async () => {
                 this.adjustVideoSize(
                     this.webcamElement.videoWidth,