I have tried
install.packages('installr')
Installing package into ‘C:/Users/Himanshu Poddar/Documents/R/win-library/3.5’ (as ‘lib’ is unspecified) Warning in install.packages : package ‘installr’ is not available (for R version 3.5.0) Warning in install.packages : unable to access index for repository https://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.5: cannot open URL 'https://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.5/PACKAGES'
install.packages("ghit")
Installing package into ‘C:/Users/Himanshu Poddar/Documents/R/win-library/3.5’ (as ‘lib’ is unspecified) Warning in install.packages : package ‘ghit’ is not available (for R version 3.5.0) Warning in install.packages : unable to access index for repository https://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.5: cannot open URL 'https://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/3.5/PACKAGES'