please update tidyverse packages #28

In an interactive fiddle created with tutorial, I get the the message "Error: could not find function str_which":

> library("stringr")
> test_v <- c("abc", "def", "cbad")
> str_which(test_v, "a.")
Error: could not find function "str_which"
> str_detect(test_v, "a.")
[1]  TRUE FALSE  TRUE
> 

Since the str_detect() function from the same package does not trigger an error, it appears that an old version of stringr is included on your server (str_which() was added to stringr in February 2017:
https://stringr.tidyverse.org/news/index.html#new-features-1 )