make consistent with keys_only

https://github.com/30-seconds/30-seconds-of-python#keys_only names parameter `flat_dict`, which avoids shadowing `dict`, seems like the right approach for here as well

snippets/values_only.md

@@ -9,8 +9,8 @@ Use `dict.values()` to return the values in the given dictionary.
 Return a `list()` of the previous result.
 
 ```py
-def values_only(dict):
-  return list(dict.values())
+def values_only(flat_dict):
+  return list(flat_dict.values())
 ```
 
 ```py