Add correct license for asciidoctor

Change If1ee984c77 introduced asciidoctor, but incorrectly set the license
as Apache2.  In fact it is licensed under MIT [1].

Add the correct license.

[1] https://github.com/asciidoctor/asciidoctor/blob/master/LICENSE.adoc

Change-Id: I7301b2efbc25daa48e63cef36259c904574c19a4
3 files changed