higher minimal R version because we depend on tibble

[RMHogervorst]

@rmhogervorst Looks nice! One thing I noticed on the CRAN page is that it says it depends on R >= 2.10 but it imports tibble, which requires R >= 3.4 so I think in practice your package also depends on R >= 3.4

https://mastodon.social/@etiennebacher/113328537460626565

Check if we can do it without tibble. Otherwise go to higher version