I had a dependency problem for MONTHS and couldn't update my Shiny app.
I just worked around it by loading the dependencies accessing R in the terminal. From there, Rstudio found them. In your case, you'd have to open terminal, type R, and run install.packages("tidyr"), then you should be able to go back into Rstudio and access it there.
Kevin, it maybe the way Rstudio is loading dependencies with Kite-Eating Tree. I was sure Thomas Lumley would be able to solve my problem in early Feb but he was totally stumped.