update code for figures based on changes made for shoot mass plot

[jeffpowell2]

See changes in Plant_Shoot_and_root_biomass_Exp1.R

line 22 to change plant names lines 64-65 and 75 to change bar widths and text position

[jeffpowell2]

I forgot to post this link, here is where I found the solution https://stackoverflow.com/questions/64400669/how-to-avoid-bars-get-wider-in-grouped-plots-when-there-is-a-missing-bar