Fix entry to_string()

Author: Alexey

src/atom/core.py

@@ -344,7 +344,7 @@ def to_string(self, version=1, encoding=None, pretty_print=None):
         if pretty_print and xmlString is not None:
             return xmlString(tree_string).toprettyxml()
 
-        return tree_string
+        return tree_string.decode('utf-8')
 
     ToString = to_string