I was able to use the library(tm) in r without problem until today, when loading tm shows:
library(tm)
The latest version of the package "slam" only works for R(>=3.4.0),so you can try either updating your R to the latest version or downloading an early version of the "slam" package.
This is a download link from CRAN for early version of "slam" package: https://cloud.r-project.org/bin/macosx/mavericks/contrib/3.3/slam_0.1-40.tgz.