Fix item number in VideoChunk ctor

Author: Djuffin

index.src.html

@@ -2639,7 +2639,7 @@
 4. For each |transferable| in |init|.{{EncodedVideoChunkInit/transfer}}:
     1. Perform [DetachArrayBuffer](https://tc39.es/ecma262/#sec-detacharraybuffer)
         on |transferable|
-3. Return |chunk|.
+5. Return |chunk|.
 
 ### Attributes ###{#encodedvideochunk-attributes}
 : <dfn attribute for=EncodedVideoChunk>type</dfn>