ghc 8 workaround for dependencies

[ilovezfs]

To get cless building under GHC 8.0.1 for Homebrew (we only typically support the latest GHC), I've needed to add a "cabal.config" file at the root of the package containing "allow-newer: base,transformers", at which point everything builds as expected. With only #2 but not also the transformers bump, I get the following:

trying: cless-0.3.0.0 (user goal)
trying: transformers-0.5.2.0/installed-0.5... (dependency of
optparse-applicative-0.12.1.0)
trying: nats-1.1 (dependency of wl-pprint-extras-3.5.0.5)
next goal: wl-pprint-terminfo (dependency of cless-0.3.0.0)
rejecting: wl-pprint-terminfo-3.7.1.3 (conflict:
transformers==0.5.2.0/installed-0.5..., wl-pprint-terminfo =>
transformers>=0.2 && <0.5)
rejecting: wl-pprint-terminfo-3.7.1.2, wl-pprint-terminfo-3.7.1.1,
wl-pprint-terminfo-3.7.1, wl-pprint-terminfo-3.7 (conflict: nats==1.1,
wl-pprint-terminfo => nats>=0.1 && <1)
rejecting: wl-pprint-terminfo-3.6, wl-pprint-terminfo-3.5,
wl-pprint-terminfo-3.4, wl-pprint-terminfo-3.3.1, wl-pprint-terminfo-3.3,
wl-pprint-terminfo-3.0.1, wl-pprint-terminfo-3.0, wl-pprint-terminfo-0.8.4,
wl-pprint-terminfo-0.8.3.2, wl-pprint-terminfo-0.8.3.1,
wl-pprint-terminfo-0.8.3, wl-pprint-terminfo-0.8.2, wl-pprint-terminfo-0.8.1,
wl-pprint-terminfo-0.8, wl-pprint-terminfo-0.7.0, wl-pprint-terminfo-0.6,
wl-pprint-terminfo-0.5.2, wl-pprint-terminfo-0.5.1, wl-pprint-terminfo-0.5,
wl-pprint-terminfo-0.4, wl-pprint-terminfo-0.3.0.1, wl-pprint-terminfo-0.3,
wl-pprint-terminfo-0.2.3, wl-pprint-terminfo-0.2.2,
wl-pprint-terminfo-0.2.1.3, wl-pprint-terminfo-0.2.1.2,
wl-pprint-terminfo-0.2.1.1, wl-pprint-terminfo-0.2.1,
wl-pprint-terminfo-0.2.0, wl-pprint-terminfo-0.1.1, wl-pprint-terminfo-0.1
(conflict: cless => wl-pprint-terminfo>=3.7)
Dependency tree exhaustively searched.

[ilovezfs]

@tanakh ping on this.