fix const list for python 2.7

Author: wangym5106

uncompyle6/semantics/n_actions.py

@@ -273,7 +273,9 @@ def n_const_list(self, node: SyntaxTree):
                     elem = elem[0]
 
                 if elem == "ADD_VALUE":
-                    if elem.optype in ("local", "name"):
+                    if self.version < (3, 0, 0):
+                        value = "%s" % repr(elem.pattr)
+                    elif elem.optype in ("local", "name"):
                         value = elem.attr
                     elif elem.optype == "const" and not isinstance(elem.attr, str):
                         value = elem.attr