fix default geom for stat_sina

[jan-glx]

[jan-glx]

Currently, the default geom for stat_sina is "sina", but GeomSina is not defined. This PR changes the default to "point", so that by default stat_sina() will match the results from geom_sina() instead of throwing an error.

---

Example current behavior:

library(ggforce)
#> Loading required package: ggplot2
ggplot(iris, aes(x = Species, y = Sepal.Length)) + stat_sina(geom="point")

ggplot(iris, aes(x = Species, y = Sepal.Length)) + stat_sina()
#> Error: Can't find `geom` called 'sina'

Example behavior with patch:

library(ggforce)
#> Loading required package: ggplot2
ggplot(iris, aes(x = Species, y = Sepal.Length)) + stat_sina(geom="point")

ggplot(iris, aes(x = Species, y = Sepal.Length)) + stat_sina()

^{Created on 2022-03-04 by the reprex package (v2.0.1)}

[thomasp85]

🙏🙏