Update _episodes/04-data-types-and-format.md

Author: orchid00

_episodes/04-data-types-and-format.md

@@ -19,7 +19,7 @@ keypoints:
     - Each column in a DataFrame has a shared data type for all rows
     - Any data type can be converted to another type
     - Null values can be discarded or changed 
-    - A DataFrame can be saved as a CSV file
+    - A DataFrame can be saved to a CSV file
 
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