update edge linewidth to compatible with the released ggplot2 (>=3.4.0)

[xiangpin]

The size of some geom in ggplot2 >= (3.4.0) had been replaced with linewidth. see the tidyverse/ggplot2#4959. The original edge_size parameters did not work to adjust the width of edge. This pr has fixed this issue.

> library(ggVennDiagram)
> x <- list(A=1:5,B=2:7,C=3:6,D=4:9)
> p1 <- ggVennDiagram(x)
> p2 <- ggVennDiagram(x, edge_size = 4)
> p1 + p2

[gaospecial]

Thanks for your contribution.