Edits and fixes based on review.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
I agree; it's canonically the Expat, but it's commonly known as "MIT" or even "X11", so I'd likely say something like `adopting the [Expat license](...) (also commonly known as the MIT or X11 license)`.