Fix when parsing NOP

Fix error when parsing NOP opcode

Author: c10udlnk

uncompyle6/parser.py

@@ -391,6 +391,10 @@ def p_stmt(self, args):
 
         returns ::= return
         returns ::= _stmts return
+        
+        # NOP
+        stmt     ::= nop_stmt
+        nop_stmt ::= NOP
 
         """
         pass