Invalidate intrinsic content size when attributed text changes

Signed-off-by: Mattt Thompson <m@mattt.me>
Merge branch 'master' of github.com:runmad/TTTAttributedLabel

# Via Rune Madsen (6) and Byunghoon Yoon (1)
* 'master' of github.com:runmad/TTTAttributedLabel:
  Add functionality for specifying an NSAttributedString to use for the truncation token with a new property: ` truncationTokenAttributedString`. This allows for a bit more customization of the truncation token, such as inclusion of different font, colours or anything else you would do with an NSAttributedString.