Clean up cabal dependencies

[MasseR]

Hello!

I noticed the project wasn't buildable with newer LTS. I started by bumping the network dependency, but ended up noticing other related things to clean up instead.

• network dependency doesn't seem to be used anywhere, so I removed it entirely. This is now one less dependency to track -> less maintenance required.
• network-uri seems to be a required dependency, unless some really old snapshot in time has the Network.URI module coming in from somewhere else. Anyway, with anything relatively recent the network-uri seems to be a mandatory dependency instead of optional.
• Re-generated the default.nix with the latest cabal information.

[schoettl]

Hi @MasseR, I just merged your commit from this PR into master. Thanks!