Remove -Werror from the cabal file

integer-simple.cabal

@@ -25,5 +25,5 @@ Library {
                 NoImplicitPrelude
     -- We need to set the package name to integer-simple
     -- (without a version number) as it's magic.
-    ghc-options: -package-name integer-simple -Wall -Werror
+    ghc-options: -package-name integer-simple -Wall
 }