Bundler could not find compatible versions for gem "mustermann":
  In snapshot (Gemfile.lock):
    mustermann (= 1.1.1)

  In Gemfile:
    oas_parser (= 0.25.4) was resolved to 0.25.4, which depends on
      mustermann-contrib (~> 1.1.1) was resolved to 1.1.1, which depends on
        mustermann (= 1.1.1)

    sinatra (~> 2.2.3) was resolved to 2.2.3, which depends on
      mustermann (~> 2.0)

Running `bundle update` will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.