Bump transformers to <0.5 to satisfy transitive dependencies of pipes-4.*

[Kludgy]

It looks like some minor updating is necessary to satisfy transitive dependencies resulting from recent versions of pipes (4.*).

Resolving dependencies...
cabal: Could not resolve dependencies:
trying: omicron-genesis-0.1.0.0 (user goal)
trying: pipes-concurrency-2.0.3 (dependency of omicron-genesis-0.1.0.0)
trying: pipes-4.1.5 (dependency of pipes-concurrency-2.0.3)
next goal: transformers (dependency of pipes-4.1.5)
rejecting: transformers-0.3.0.0/installed-570... (conflict: mtl =>
transformers==0.4.*)
trying: transformers-0.4.3.0
next goal: pipes-network-tls (dependency of omicron-genesis-0.1.0.0)
rejecting: pipes-network-tls-0.2.1 (conflict: transformers==0.4.3.0,
pipes-network-tls => transformers(>=0.2 && <0.4))
rejecting: pipes-network-tls-0.2.0 (conflict: pipes==4.1.5, pipes-network-tls
=> pipes(>=4.0 && <4.1))
rejecting: pipes-network-tls-0.1.1.0, 0.1.0.0 (conflict: pipes==4.1.5,
pipes-network-tls => pipes(>=3.3 && <3.4))
Dependency tree exhaustively searched.