allow use of Rtools 3.5 for R 3.6 (devel)
allow use of Rtools 3.5 for R 3.6 (devel)

JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio