feat: use new concerns syntax

lib/closure_tree/digraphs.rb

@@ -11,7 +11,7 @@ def to_digraph_label
       _ct.has_name? ? read_attribute(_ct.name_column) : to_s
     end
 
-    module ClassMethods
+    class_methods do
       # Renders the given scope as a DOT digraph, suitable for rendering by Graphviz
       def to_dot_digraph(tree_scope)
         id_to_instance = tree_scope.reduce({}) { |h, ea| h[ea.id] = ea; h }

lib/closure_tree/finders.rb

@@ -50,7 +50,7 @@ def without_self(scope)
       scope.without_instance(self)
     end
 
-    module ClassMethods
+    class_methods do
 
       def without_instance(instance)
         if instance.new_record?

lib/closure_tree/hash_tree.rb

@@ -6,7 +6,7 @@ def hash_tree(options = {})
       _ct.hash_tree(self_and_descendants, options[:limit_depth])
     end
 
-    module ClassMethods
+    class_methods do
 
       # There is no default depth limit. This might be crazy-big, depending
       # on your tree shape. Hash huge trees at your own peril!

lib/closure_tree/hierarchy_maintenance.rb

@@ -104,7 +104,7 @@ def delete_hierarchy_references
       end
     end
 
-    module ClassMethods
+    class_methods do
       # Rebuilds the hierarchy table based on the parent_id column in the database.
       # Note that the hierarchy table will be truncated.
       def rebuild!

lib/closure_tree/numeric_deterministic_ordering.rb

@@ -42,7 +42,7 @@ def self_and_descendants_preordered
         .reorder(self.class._ct_sum_order_by(self))
     end
 
-    module ClassMethods
+    class_methods do
 
       # If node is nil, order the whole tree.
       def _ct_sum_order_by(node = nil)