fix type check failure (Int32 vs Int64)

Hello,

I am trying to compile stackage on windows, and I get the following compilation error:

    [11 of 13] Compiling Stackage.ServerBundle ( Stackage\ServerBundle.hs, dist\build\Stackage\ServerBundle.o )
    
    Stackage\ServerBundle.hs:27:28:
        Couldn't match type `Int32' with `Int64'
        Expected type: Tar.EpochTime
          Actual type: Int32
        In the expression: t
        In the first argument of `(<$>)', namely `(\ (CTime t) -> t)'

I fixed it with a `fromIntegral`.