Need to update VAST4 with newer codec spec reference

[amitshetty]

Posting for Tay @ itv

Hi Amit, Greetings from the UK. I am working with a group of European broadcasters to ratify VAST as the interoperability standard for commercial TV. We have noticed that VAST 4.1 and VAST 4.2 are referencing obsolete reference: http://tools.ietf.org/html/rfc4281 (VAST 4.1 p53 and p54) This has been superseded by https://tools.ietf.org/html/rfc6381 We'd appreciate if you could correct this for future releases. Best regards, Tay