network-uri flag fix
network-uri flag fix

Without this change, I got the following error when compiling:

Configuring hackage-server-0.5.0...
Building hackage-server-0.5.0...
Preprocessing executable 'hackage-server' for hackage-server-0.5.0...

Main.hs:40:8:
    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.

edsko/hackage-server,tkvogt/hackage-server,tkvogt/hackage-server,dzackgarza/hackage-server,edsko/hackage-server,chrisdotcode/hackage-server,agrafix/hackage-server,grayjay/hackage-server,grayjay/hackage-server,ocharles/hackage-server,dzackgarza/hackage-server,snoyberg/hackage-server,erantapaa/hackage-server,erantapaa/hackage-server,ocharles/hackage-server,chrisdotcode/hackage-server,snoyberg/hackage-server,agrafix/hackage-server