haddock-library: require GHC >= 7.4

`Data.Monoid.<>` was added in base-4.5/GHC-7.4

Closes #394

Signed-off-by: Mateusz Kowalczyk <fuuzetsu@fuuzetsu.co.uk>

haddock-library/haddock-library.cabal

@@ -21,7 +21,7 @@ library
   default-language:     Haskell2010
 
   build-depends:
-      base >= 4.3 && < 4.9
+      base >= 4.5 && < 4.9
     , bytestring
     , transformers
     , deepseq