Attempt to fix import issue when unpickling in the standalone parser

Author: erezsh

lark/grammar.py

@@ -60,7 +60,7 @@ class NonTerminal(Symbol):
     def serialize(self, memo=None) -> Dict[str, Any]:
         # TODO this is here because self.name can be a Token instance.
         #      remove this function when the issue is fixed. (backwards-incompatible)
-        return {'name': str(self.name)}
+        return {'name': str(self.name), '__type__': 'NonTerminal'}
 
 
 class RuleOptions(Serialize):