style: add missing whitespaces in plot.OutputsModel

Resf #112
3 jobs for 122-review-the-x-axis-management-of-the-plot-outputsmodel in 9 minutes and 7 seconds (queued for 10 seconds)
Status Name Job ID Coverage
  Check
passed check_as_cran_patched #186639

00:02:41

passed check_not_cran_patched #186638

00:05:21

 
  Regression
passed regression_patched #186640

00:01:04