oxford comma

Co-authored-by: Marianne Corvellec <marianne.corvellec@ens-lyon.org>

Author: JeremyPike

episodes/03-skimage-images.md

@@ -388,7 +388,7 @@ range 0-255 of an 8-bit pixel). The results should look like this:
 
 ![](fig/sudoku-gray.png){alt='Modified Su-Do-Ku puzzle'}
 
-*Hint: the `cmap`, `vmin` and `vmax` parameters of `matplotlib.pyplot.imshow`
+*Hint: the `cmap`, `vmin`, and `vmax` parameters of `matplotlib.pyplot.imshow`
 will be needed to display the modified image as desired. See the [matplotlib
 documentation](https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.imshow.html) 
 for more details on `cmap`, `vmin` and `vmax`.*