🐛 FIX: `_Entities.__contains__` (#69)

diff --git a/markdown_it/common/entities.py b/markdown_it/common/entities.py
index e08fdca..f1488d5 100644
--- a/markdown_it/common/entities.py
+++ b/markdown_it/common/entities.py
@@ -15,7 +15,7 @@
         return DATA[name]
 
     def __contains__(self, name):
-        name in DATA
+        return name in DATA
 
 
 entities = _Entities()