Update interfaces/encrypted-media.idl (#26992)

Source: https://github.com/w3c/webref/blob/bfb1aaf/ed/idl/encrypted-media.idl
Build: https://travis-ci.org/w3c/webref/builds/210346230

Author: autofoolip

interfaces/encrypted-media.idl

@@ -65,7 +65,7 @@ enum MediaKeySessionType {
     iterable<BufferSource,MediaKeyStatus>;
     readonly        attribute unsigned long size;
     boolean has (BufferSource keyId);
-    any     get (BufferSource keyId);
+    (MediaKeyStatus or undefined)     get (BufferSource keyId);
 };
 
 enum MediaKeyStatus {