Update usage of RubyTree to avoid deprecated methods

lib/file_tree.rb

@@ -45,8 +45,8 @@ class FileTree
       icon: node_icon(node),
       id: node.content.try(:ancestor_id),
       state: {
-        disabled: !node.is_leaf?,
-        opened: !node.is_leaf?,
+        disabled: !node.leaf?,
+        opened: !node.leaf?,
       },
       text: node.name,
     }
@@ -54,7 +54,7 @@ class FileTree
   private :map_to_js_tree
 
   def node_icon(node)
-    if node.is_leaf? && !node.is_root?
+    if node.leaf? && !node.root?
       file_icon(node.content)
     else
       folder_icon

spec/lib/file_tree_spec.rb

@@ -90,7 +90,7 @@ describe FileTree do
     end
 
     it 'creates tree nodes for intermediary path segments' do
-      expect(file_tree.instance_variable_get(:@root).reject(&:content).reject(&:is_root?).map(&:name)).to eq(files.first.path.split('/'))
+      expect(file_tree.instance_variable_get(:@root).reject(&:content).reject(&:root?).map(&:name)).to eq(files.first.path.split('/'))
     end
   end