The key lines are around line 23. In the good run, I install stringi before using RSPM, in the bad run, I install stringi with RSPM. In the bad run, travis bombs with the error:
> Rscript -e "stringi::stri_c(1)"
Error in dyn.load(file, DLLpath = DLLpath, ...) :
unable to load shared object '/home/travis/R/Library/stringi/libs/stringi.so':
libicui18n.so.60: cannot open shared object file: No such file or directory