Object Size ECDF page in documents has incorrect function name in example.

[hkmanching]

Describe the bug
The wrong function name is called in example on page (https://plantcv.readthedocs.io/en/stable/visualize_obj_size_ecdf/), so it won't work.

Uses: fig_ecdf = pcv.visualize.ecdf.obj_size(mask=mask)
Should be: fig_ecdf = pcv.visualize.obj_size_ecdf(mask=mask)

[HaleySchuhl]

@hkmanching thank you for bringing this to our attention. I can fix that.

[HaleySchuhl]

@all-contributors please add @hkmanching for bug

[allcontributors]

@HaleySchuhl

I've put up a pull request to add @hkmanching! 🎉