Refactoring suppoted in DLTK 1.0?

I downloaded ruby DLTK from HERE
the bundle package.

see very simple test program below,

class ClassTest
def initialize(name_str)
@name_str = name_str

def name
return @name_str

a =“Akira”)

Trying to change field name “name_str” to “name_string”
I put my cursor to @name_str in my ClassTest class
and choose “Refactor” in menubar and then choose “Rename”

However, as I did not expect, the error message

“Operation unavailable on the current selection …” comes out.

What should I do to rename the field name?
rename refactoring is very useful feature.