Fix builds on Hackage

[fizruk]

Currently, uploaded packages fail to build on Hackage (see here for free-foil-0.0.3):

Resolving dependencies...
Error: cabal: Could not resolve dependencies:
[__0] trying: free-foil-0.0.3 (user goal)
[__1] next goal: template-haskell (dependency of free-foil)
[__1] rejecting: template-haskell-2.20.0.0/installed-2.20.0.0 (conflict:
free-foil => template-haskell>=2.21.0.0)
[__1] rejecting: template-haskell-2.22.0.0, template-haskell-2.21.0.0,
template-haskell-2.20.0.0, template-haskell-2.19.0.0,
template-haskell-2.18.0.0, template-haskell-2.17.0.0,
template-haskell-2.16.0.0, template-haskell-2.15.0.0,
template-haskell-2.14.0.0, template-haskell-2.13.0.0,
template-haskell-2.12.0.0, template-haskell-2.11.1.0,
template-haskell-2.11.0.0, template-haskell-2.10.0.0,
template-haskell-2.9.0.0, template-haskell-2.8.0.0, template-haskell-2.7.0.0,
template-haskell-2.6.0.0, template-haskell-2.5.0.0, template-haskell-2.4.0.1,
template-haskell-2.4.0.0, template-haskell-2.3.0.1, template-haskell-2.3.0.0,
template-haskell-2.2.0.0 (constraint from non-upgradeable package requires
installed instance)
[__1] fail (backjumping, conflict set: free-foil, template-haskell)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: template-haskell, free-foil

[fizruk]

Apparently, we need to support older template-haskell.