Update filter_unique.md

snippets/filter_unique.md

@@ -12,8 +12,7 @@ Use list comprehension to create a list containing only the non-unique values.
 from collections import Counter
 
 def filter_unique(lst):
-  counter = Counter(lst)
-  return [item for item, count in counter.items() if count > 1]
+  return [item for item, count in Counter(lst).items() if count > 1]
 ```
 
 ```py