style: add missing whitespaces in plot.OutputsModel

Resf #112
3 jobs for 122-review-the-x-axis-management-of-the-plot-outputsmodel in 10 minutes and 8 seconds (queued for 8 seconds)
Status Name Job ID Coverage
  Check
passed check_as_cran_patched #186642

00:03:38

passed check_not_cran_patched #186641

00:05:22

 
  Regression
passed regression_patched #186643

00:01:08