Add support for HaskellNet 0.6 (#28)

Author: vzaliva

HaskellNet-SSL.cabal

@@ -44,7 +44,7 @@ library
                        data-default
   else
     build-depends:     base >= 4 && < 5,
-                       HaskellNet >= 0.3 && < 0.6,
+                       HaskellNet >= 0.3 && < 0.7,
                        tls >= 1.2 && < 1.6,
                        connection >= 0.2.7 && < 0.4,
                        bytestring,