Update AnonCreds Data Integrity Proof docs for the new cryptosuite value

[swcurran]

PR #317 changed the cryptosuite values for the AnonCreds Data integrity proof to be the same for all three instances of a proofValues (VC, VCs in a Presentation, VP). Adding this issue as a reminder to make sure the documentation gets updated in this Repo (the design document) and in the AnonCreds Spec.