Update cucumber dependency

In the process, we remove our cucumber docstrings monkey patch. It
does not work anymore and it was not a so good idea.

features/support/env_cucumber_doc_string.rb

@@ -1,23 +0,0 @@
-require 'cucumber/formatter/pretty'
-
-module Cucumber
-  module Ast
-    class DocString
-      alias :old_initialize :initialize
-
-      def initialize(string, content_type)
-        old_initialize(string + "\n", content_type)
-      end
-    end
-  end
-
-  module Formatter
-    class Pretty
-      alias :old_doc_string :doc_string
-
-      def doc_string(string)
-        old_doc_string(string.chomp)
-      end
-    end
-  end
-end