Replace size argument with linewidth for geom_line and geom_ridgeline

[heavywatal]

This is a follow-up of f38d063 and 89c1228.

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (621d52a) 98.53% compared to head (d99ac48) 98.55%.
Report is 20 commits behind head on master.

❗ Current head d99ac48 differs from pull request most recent head 90f8e1a. Consider uploading reports for the commit 90f8e1a to get more accurate results

Files	Patch %	Lines
R/bayesplot-helpers.R	66.66%	1 Missing ⚠️
R/mcmc-intervals.R	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #314      +/-   ##
==========================================
+ Coverage   98.53%   98.55%   +0.02%     
==========================================
  Files          35       35              
  Lines        4972     4992      +20     
==========================================
+ Hits         4899     4920      +21     
+ Misses         73       72       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jgabry]

Thanks for catching these ones I missed previously