Use new trias package version to define width and height GAM figures

[damianooldoni]

Specify width and height where apply_gam() function is used so that width and height of the saved plot (png files) are not dependent on the RStudio window pane, which is never defined a priori of course.

To do so, use trias package version 2.3.0 or higher. This version is the latest at the moment of writing. See trias-project/trias#129.