Log Message:
py-bleach: updated to 3.1.0

Version 3.1.0:
**Features**
* Add recognized_tags argument to the linkify Linker class. This
  fixes issues when linkifying on its own and having some tags get escaped.
  It defaults to a list of HTML5 tags.

**Bug fixes**
* Add six>=1.9 to requirements.
* Fix cases where attribute names could have invalid characters in them.
* Fix problems with LinkifyFilter not being able to match links
  across &.
* Fix InputStreamWithMemory when the BleachHTMLParser is
  parsing meta tags.
* Fix doctests.