Fixed all warnings, all travis tests good

[henrylaxen]

I fixed the following 5 warnings that popped up when I compiled the git version with ghc-8.8.3:

src/Snap/Internal/Http/Server/Address.hs:70:5: warning: [-Woverlapping-patterns]
Pattern match is redundant
In a case alternative: _ -> ...
|
70 | _ -> fail "Unsupported address type"
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/Snap/Internal/Http/Server/Session.hs:38:1: warning: [-Wunused-imports]
The import of ‘Data.Monoid’ is redundant
except perhaps to import instances from ‘Data.Monoid’
To import instances alone, use: import Data.Monoid()
|
38 | import Data.Monoid ((<>))
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/Snap/Internal/Http/Server/Socket.hs:178:40: warning: [-Wdeprecations]
In the use of ‘fdSocket’
(imported from Network.Socket, but defined in network-3.1.1.1:Network.Socket.Types):
Deprecated: "Use withFdSocket or unsafeFdSocket instead"
|
178 | go fileFd = do sockFd <- Fd fmap fdSocket sock
| ^^^^^^^^

src/Snap/Internal/Http/Server/Session.hs:38:1: warning: [-Wunused-imports]
The import of ‘Data.Monoid’ is redundant
except perhaps to import instances from ‘Data.Monoid’
To import instances alone, use: import Data.Monoid()
|
38 | import Data.Monoid ((<>))
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/Snap/Internal/Http/Server/Socket.hs:178:40: warning: [-Wdeprecations]
In the use of ‘fdSocket’
(imported from Network.Socket, but defined in network-3.1.1.1:Network.Socket.Types):
Deprecated: "Use withFdSocket or unsafeFdSocket instead"
|
178 | go fileFd = do sockFd <- Fd fmap fdSocket sock
| ^^^^^^^^