Update redsift.cabal to include network-uri.

This is to solve:

Redsift/SignUrl.hs:9:8:
    Could not find module 'Network.URI'
    It is a member of the hidden package 'network-uri-2.6.0.1'.
    Perhaps you need to add 'network-uri' to the build-depends in your .cabal file.
    Use -v to see a list of the files searched for.
cabal: Error: some packages failed to install:
redsift-0.1.0 failed during the building phase. The exception was:
ExitFailure 1