fix haml linter declaration

This is necessary in order to boot delayed_job -_-
Without this, it attempts to inherit a missing class

lib/linters/application_name_linter.rb

@@ -1,4 +1,5 @@
-module HamlLint
+if defined?(HamlLint)
+  module HamlLint
     class Linter::ApplicationNameLinter < Linter
       include LinterRegistry
 
@@ -43,4 +44,5 @@ module HamlLint
         document.source_lines[node.line - 1]
       end
     end
+  end
 end