Change a double-quoted string to single-qouted.

Change-Id: I74a0057bebfd469028468299a1da3c84b24f00d9
diff --git a/adaptive/dash_player.js b/adaptive/dash_player.js
index b2c99e1..2c81ac4 100644
--- a/adaptive/dash_player.js
+++ b/adaptive/dash_player.js
@@ -898,7 +898,7 @@
   var key = key_id;
   this.log('Adding key for the following ID: ');
   this.log(key_id);
-  this.videoElement.webkitAddKey("webkit-org.w3.clearkey", key, key_id);
+  this.videoElement.webkitAddKey('webkit-org.w3.clearkey', key, key_id);
 };
 
 /**