Work around cabal conflict for transformers 0.5

A temporary workaround until `exceptions` can be built with
`transformers` 0.5. The work is already in progress but it depends on
some bigger changes in transformers-compat
(see https://github.com/ekmett/exceptions/pull/51).

compiler/bond.cabal

@@ -43,7 +43,8 @@ library
                     mtl >= 2.1,
                     parsec >= 3.1,
                     shakespeare >= 2.0,
-                    text >= 0.11
+                    text >= 0.11,
+                    transformers < 0.5
   ghc-options:      -Wall
   exposed-modules:  Language.Bond.Parser
                     Language.Bond.Util