Added natsort to the dependency list in environment.yml

[jaroslawjanas]

• fix Package missing in environment.yml (conda) #641

This adds missing natsort to the list of dependencies in environment.yml.
Versioning is kept the same as in requirements.txt.

[axu2]

@jaroslawjanas Do you want to add natsort[fast] instead? (I've don't use conda.)

[jaroslawjanas]

@jaroslawjanas Do you want to add natsort[fast] instead? (I've don't use conda.)

Sure. I just checked if it works, all good on my side.