[w3c/webauthn] a525ed: Stop using .gitattributes from w3c/html

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: a525ed329df9c427ecb6b3eae0f0dfd40a3f626b
      https://github.com/w3c/webauthn/commit/a525ed329df9c427ecb6b3eae0f0dfd40a3f626b
  Author: J.C. Jones <jjones@mozilla.com>
  Date:   2016-07-13 (Wed, 13 Jul 2016)

  Changed paths:
    M .gitattributes

  Log Message:
  -----------
  Stop using .gitattributes from w3c/html

Basically, all we need from this file is to define what `.bs` is, so this
commit trims down to that. The rest is unnecessary, and causing issues.