fix typo line 56 (#307)

Co-authored-by: Ronan Stokes <[email protected]>

docs/source/using_standard_datasets.rst

@@ -53,7 +53,7 @@ For the simplest use, you can simply select a standard dataset and generate a da
 
 .. code-block:: python
 
-   import dbldatagen as df
+   import dbldatagen as dg
    df = dg.Datasets(spark, "basic/user").get().build()
    display(df)