Revert maybe_placeholders to be False by default.. It should be changed in a major release, not 0.8 (Issue #515)

lark/lark.py

@@ -64,7 +64,7 @@ class LarkOptions(Serialize):
         'ambiguity': 'auto',
         'propagate_positions': False,
         'lexer_callbacks': {},
-        'maybe_placeholders': True,
+        'maybe_placeholders': False,
         'edit_terminals': None,
     }