Merge pull request #1514 from virtuacoplenny/lenny/video-preview-mute-string

fix: change string displayed when previewing a muted video input

lang/main.json

         "speakerTime": "Speaker Time"
     },
     "deviceSelection": {
+        "currentlyVideoMuted": "Video is currently muted",
         "deviceSettings": "Device settings",
         "noOtherDevices": "No other devices available",
         "selectADevice": "Select a device",

react/features/device-selection/components/VideoInputPreview.js

                     className = 'video-input-preview-display flipVideoX'
                     ref = { this._setVideoElement } />
                 <div className = 'video-input-preview-muted'>
-                    { this.props.t('videothumbnail.muted') }
+                    { this.props.t('deviceSelection.currentlyVideoMuted') }
                 </div>
             </div>
         );