README example uses non-existing method

[nbigaouette-eai]

The README has:

    let Mnist { trn_img, trn_lbl, .. } = MnistBuilder::new()
         .image_format_28x28()
         .label_format_1x1()
[...]

but both image_format_28x28() and label_format_1x1() are invalid methods.

They should probably be removed from the example (as is the case in the documentation).

[davidMcneil]

Thanks! That example was from an outdated version.