Update transformers bounds

Bump `transformers` upper bounds from 0.5 to 0.6 for compatibility with Stackage Nightly.

Author: akhra

sdl2.cabal

@@ -1,5 +1,5 @@
 name:                sdl2
-version:             2.1.2
+version:             2.1.2.1
 synopsis:            Both high- and low-level bindings to the SDL library (version 2.0.2).
 description:
   This package contains bindings to the SDL 2 library, in both high- and
@@ -113,7 +113,7 @@ library
     linear >= 1.10.1.2 && < 1.21,
     StateVar >= 1.1.0.0 && < 1.2,
     text >= 1.1.0.0 && < 1.3,
-    transformers >= 0.2 && < 0.5,
+    transformers >= 0.2 && < 0.6,
     vector >= 0.10.9.0 && < 0.12
 
   default-language: