undefined method `ruby2_keywords' with version 1.1.0

[Annih]

Hello,

Since release of mustermann 1.1.0 my application is failing with the following error:

NoMethodError: undefined method `ruby2_keywords' for Mustermann::AST::Parser:Class
  .bundle/gems/mustermann-1.1.0/lib/mustermann/ast/parser.rb:67:in `<class:Parser>'
  .bundle/gems/mustermann-1.1.0/lib/mustermann/ast/parser.rb:11:in `<module:AST>'
  .bundle/gems/mustermann-1.1.0/lib/mustermann/ast/parser.rb:8:in `<module:Mustermann>'
  .bundle/gems/mustermann-1.1.0/lib/mustermann/ast/parser.rb:6:in `<top (required)>'
  .bundle/gems/mustermann-1.1.0/lib/mustermann/ast/pattern.rb:2:in `require'
  .bundle/gems/mustermann-1.1.0/lib/mustermann/ast/pattern.rb:2:in `<top (required)>'
  .bundle/gems/mustermann19-0.4.4/lib/mustermann/grape.rb:1:in `require'
  .bundle/gems/rack-2.0.8/lib/rack/builder.rb:55:in `instance_eval'
  .bundle/gems/rack-2.0.8/lib/rack/builder.rb:55:in `initialize'
  my-project/config.ru:in `new'
  my-project/config.ru:in `<main>'