Try excluding uverb cookbook from pre 8.6.1 builds

Author: Gaël Deest

doc/cookbook/uverb/uverb.cabal

@@ -28,6 +28,8 @@ executable cookbook-uverb
                      , swagger2
                      , wai
                      , warp
-  default-language:    Haskell2010
+  if impl(ghc < 8.6.1)
+        buildable: False
+  default-language: Haskell2010
   ghc-options:         -Wall -pgmL markdown-unlit
   build-tool-depends:  markdown-unlit:markdown-unlit