Block newer cassava commercialhaskell/stack#3345

Author: snoyberg

build-constraints.yaml

@@ -3318,6 +3318,9 @@ packages:
         # https://github.com/fpco/stackage/issues/2740
         - fgl < 5.6
 
+        # https://github.com/commercialhaskell/stack/issues/3345
+        - cassava < 0.5.1.0
+
 # end of packages
 
 # Package flags are applied to individual packages, and override the values of
@@ -3415,7 +3418,7 @@ package-flags:
         win32-2-5: false
 
     cassava:
-        bytestring--lt-0_10_4: false
+        pre-bytestring-0-10-4: false
 
 # end of package-flags