我无法安装tm软件包

Question

在R中安装tm软件包时遇到大问题

install.packages("tm")

Warning in install.packages :
  package ‘tm’ is not available (for R version 3.5.2)
Warning in install.packages :
  unable to access index for repository https://cran.rstudio.com/bin/windows/contrib/3.5:
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.5/PACKAGES'