Remove zlib upper bound

yesod-bin/yesod-bin.cabal

@@ -61,7 +61,7 @@ executable             yesod
                      , blaze-builder      >= 0.2.1.4      && < 0.5
                      , filepath           >= 1.1
                      , process
-                     , zlib               >= 0.5          && < 0.6
+                     , zlib               >= 0.5
                      , tar                >= 0.4          && < 0.5
                      , system-filepath    >= 0.4          && < 0.5
                      , system-fileio      >= 0.3          && < 0.4