Allow dplyr group_by to work w/ ggplot2 geom_path() to avoid mangled 🦃s

dplyr `group_by`
![thanksggiving](https://user-images.githubusercontent.com/831732/33181689-2bfcd518-d03f-11e7-8dda-6c32536b0942.png)
http://rpubs.com/maraaverick/thanksggiving

ggplot2 `group_by`
![tgives_turkey](https://user-images.githubusercontent.com/831732/33181694-317af312-d03f-11e7-8b98-e153d1cde21e.png)
http://rpubs.com/maraaverick/thanksgiving