Update cabal-doctest.cabal

[amcphail]

Bump upper Cabal dependency version

[phadej]

I'm sorry, but I have to reject htis.
Cabal-2.1 isn't out yet. Use allow-newer.

Also <= is fishy. We'll have <2.3, when time is right.

I won't make any speculative releases. See https://github.com/hvr/head.hackage if we'll actually need to do some changes for testing GHC HEAD.

[RyanGlScott]

As it turns out, GHC HEAD now depends on a newer version of Cabal which doesn't currently build with the latest cabal-doctest on Hackage (1.0.3). In the meantime, I've submitted a patch at head.hackage.

[RyanGlScott]

..never mind. As explained here, Cabal-2.1 does indeed build with cabal-doctest-1.0.4—for the time being, at least.

When Cabal-2.2 is finalized, we'll bump the upper version bound. It's better to be safe than sorry with Cabal, given its relatively volatile API.

[RyanGlScott]

Superseded by #36.