It looks like you have your CRAN repo option set a little bit oddly, with http://cran.rstudio.com/src/constrib where you should have https://cran.rstudio.com/.
Try adding the following to your .Rprofile and restarting RStudio, and see what happens:
.First <- function() {
options(
repos = c(CRAN = "https://cran.rstudio.com/")
)
}