documentation examples no longer work

[friendly]

With ggpcp 0.2.0, many examples in the README no longer work:
What has happened?

data(flea, package = "GGally")
flea %>%
  ggplot(aes(colour = species)) + 
  geom_pcp(aes(vars=vars(species, 2:7, species)))

Gives:

Error in `geom_pcp()`:
! Problem while computing aesthetics.
i Error occurred in the 1st layer.
Caused by error in `check_aesthetics()`:
! Aesthetics must be either length 1 or the same as the data (74)
x Fix the following mappings: `vars`
Run `rlang::last_trace()` to see where the error occurred.