add rake task to exit with error code when fail

lib/brakeman/brakeman.rake

@@ -7,4 +7,11 @@ namespace :brakeman do
     files = args[:output_files].split(' ') if args[:output_files]
     Brakeman.run :app_path => ".", :output_files => files, :print_report => true
   end
+
+  desc "Check your code with Brakeman"
+  task :check do
+    require 'brakeman'
+    result = Brakeman.run app_path: '.', print_report: true
+    exit Brakeman::Warnings_Found_Exit_Code unless result.filtered_warnings.empty?
+  end
 end