[build2] 7.0 depends on 7.0 in master

[Boris Kolpackov]

Kalle Møller <build2.org at k-moeller.dk> writes:

> I might just be me not fully understand the underlying, but since the
> master branch requires 7.0 to be built, the 6.1 release will not be able to
> upgrade to 7.0 once it releases? Unless 7.0 builds itself instead of using
> 6.1?

Yes, now during early development we make a lot of breaking changes so
you have to bootstrap every release from scratch.

Boris