GM: now that we use MD5 instead of CityHash, the JSON should say so

GM: now that we use MD5 instead of CityHash, the JSON should say so
(this should have been part of https://code.google.com/p/skia/source/detail?r=8992 )

R=bungeman@google.com

Review URL: https://codereview.chromium.org/14758003

git-svn-id: http://skia.googlecode.com/svn/trunk@9038 2bbb7eff-a529-9590-31e7-b0007b416f81