Update deep_flatten.md

snippets/deep_flatten.md

@@ -18,7 +18,7 @@ def spread(arg):
 def deep_flatten(arr):
     result = []
     result.extend(
-        spread(list(map(lambda x: deep(x) if type(x) == list else x, arr))))
+        spread(list(map(lambda x: deep_flatten(x) if type(x) == list else x, arr))))
     return result
 ```