fix warning message: deprecated arguments

[Yunuuuu]

adjust to ggplot2 parameters

[clauswilke]

Please file an issue first, then we can discuss an appropriate PR.

[Yunuuuu]

Sorry, I'll open a issue, and now, I'll give a description of the problem this commit fixed. When I used function (like scater::plotColData) which internally called theme function from cowplot there always prompts some annoying message by ggplot2 deprecated arguments size from element_text() and element_rect(). A minimal example:

library(ggplot2)
library(cowplot)


ggplot(mtcars) +
    geom_point(aes(mpg, drat)) +
    theme_cowplot()

Warning messages:
1: The `size` argument of `element_line()` is
deprecated as of ggplot2 3.4.0.
ℹ Please use the `linewidth` argument instead.
ℹ The deprecated feature was likely used in the
  cowplot package.
  Please report the issue at
  <https://github.com/wilkelab/cowplot/issues>.
This warning is displayed once every 8 hours.
Call `lifecycle::last_lifecycle_warnings()` to
see where this warning was generated. 
2: The `size` argument of `element_rect()` is
deprecated as of ggplot2 3.4.0.
ℹ Please use the `linewidth` argument instead.
ℹ The deprecated feature was likely used in the
  cowplot package.
  Please report the issue at
  <https://github.com/wilkelab/cowplot/issues>.
This warning is displayed once every 8 hours.
Call `lifecycle::last_lifecycle_warnings()` to
see where this warning was generated. 

[Yunuuuu]

fix #190

[Yunuuuu]

And maybe we shoud add a dependencies of ggplot2 (> 3.4.0) ?

[Yunuuuu]

The latest ggplot2 has been published: https://github.com/tidyverse/ggplot2/releases/tag/v3.4.0

[clauswilke]

Apologies for the absence on my end. Could you do the following, and then I'm happy to merge:

1. Update the ggplot2 dependency so it's clear we will need >= 3.4.0 going forward
2. Make an entry in NEWS.md describing the changes. I encourage you to acknowledge your contribution as described here.

Also, can you confirm that you have searched the codebase and found all instances that require this change? Thanks for your efforts!

[Yunuuuu]

I have searched element_line and element_rect use vscode. all related size argument have beee substituted by linewidth

[clauswilke]

Thanks!