Set default videoConstraints (#4070)

* Set default videoConstraints

* Update packages/@uppy/webcam/src/Webcam.jsx

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

packages/@uppy/webcam/src/Webcam.jsx

@@ -99,6 +99,7 @@ export default class Webcam extends UIPlugin {
       mirror: true,
       showVideoSourceDropdown: false,
       facingMode: 'user', // @TODO: remove in the next major
+      videoConstraints: undefined,
       preferredImageMimeType: null,
       preferredVideoMimeType: null,
       showRecordingLength: false,