DUB registry is now Boost licensed

[Seb]

Just a quick heads-up at all those people how were considering of 
rolling a customized dub in-house (or on your favorite PaaS 
provider).
You can now modify it without needing to publish all your patches 
which the GPL license before required.
Of course, improvement patches (aka PRs) are still very welcome 
;-)

See also:

https://github.com/dlang/dub-registry/pull/272