[Glitch] Fix new audio player features not working on Safari

Port 51b5bb5301 to glitch-soc

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

app/javascript/flavours/glitch/features/audio/index.js

@@ -254,8 +254,9 @@ class Audio extends React.PureComponent {
   }
 
   _initAudioContext () {
-    const context  = new AudioContext();
-    const source   = context.createMediaElementSource(this.audio);
+    const AudioContext = window.AudioContext || window.webkitAudioContext;
+    const context      = new AudioContext();
+    const source       = context.createMediaElementSource(this.audio);
 
     this.visualizer.setAudioContext(context, source);
     source.connect(context.destination);