Relaxed upper version bound for transformers.

Author: svenpanne

OpenGLRaw.cabal

@@ -700,7 +700,7 @@ library
     fixed        >= 0.2     && < 0.4,
     half         >= 0.2.2.1 && < 0.4,
     text         >= 0.1     && < 1.3,
-    transformers >= 0.2     && < 0.6
+    transformers >= 0.2     && < 0.7
   default-language: Haskell2010
   ghc-options: -Wall
   if impl(ghc > 8)