Update vector-bytestring.cabal

The library and the benchmarks build fine with ghc-7.8 if base is upgraded. Something has happened to QuickCheck though, so the tests don't build: 


    tests/QuickCheckUtils.hs:32:48:
      Couldn't match expected type ‘Gen a0’ with actual type ‘Property’
      In the second argument of ‘resize’, namely ‘(property p)’
      In the expression: resize (f sz) (property p)

There are also a number of warnings like 

    Module ‘Foreign’ does not export ‘unsafePerformIO’

and

    In the use of ‘bitSize’
    (imported from Foreign, but defined in Data.Bits):
    Deprecated: "Use 'bitSizeMaybe' or 'finiteBitSize' instead"