Remove unnecessary .compact call (#562)

The `.compact` method is used to remove nil elements from an array.
However, in this context, it is unnecessary because the `.map` operation
is already creating an array of strings, and there's no `nil` values
that could be removed

Author: tagliala

lib/arbre/html/attributes.rb

@@ -6,7 +6,7 @@ class Attributes < Hash
       def to_s
         flatten_hash.compact.map do |name, value|
           "#{html_escape(name)}=\"#{html_escape(value)}\""
-        end.compact.join ' '
+        end.join ' '
       end
 
       protected