Bug if pixel_size = 1.0 um

[ahillsley]

There is a bug in shrimPy/mantis/cli/estimate-stitch.py lines 88-92. If the pixel size is set to 1.0 um (the default) rather than show the input prompt it returns an error message " TypeError: input expected at most 1 argument, got 3". I believe that this is caused by the prompt being made up of 3 separate strings. Should be a really easy fix, Thanks!