dfr lowercase for dataframe

Lowercase the strings in the column.

Signature

> dfr lowercase

Examples

Modifies strings to lowercase

> [Abc aBc abC] | dfr into-df | dfr lowercase
╭───┬─────╮
│ # │  0  │
├───┼─────┤
│ 0 │ abc │
│ 1 │ abc │
│ 2 │ abc │
╰───┴─────╯