def call
    return unless @bin_dir.directory?

    each_binstub do |binstub|
      @bad_binstubs << binstub if binstub.bad_shebang?
    end

    warn unless @bad_binstubs.empty?
  end
Checks all binstubs in the directory for a
bad shebang line. If any are present
a warning is created on the passed in `warn_object`