Relaxed upper version bound for transformers.

Author: svenpanne

OpenGL.cabal

@@ -152,7 +152,7 @@ library
     bytestring   >= 0.9   && < 0.11,
     containers   >= 0.3   && < 0.6,
     text         >= 0.1   && < 1.3,
-    transformers >= 0.2   && < 0.5,
+    transformers >= 0.2   && < 0.6,
     ObjectName   >= 1.1   && < 1.2,
     StateVar     >= 1.1   && < 1.2,
     OpenGLRaw    >= 2.6.1 && < 2.7,