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:
I having been woking with Rstudio environment for past 3 months and I have installed packages like ggplot2, hexbin, dplyr, hflights and so on in my system....
But I am facing this issue only for the last 3 days....