Installation of dust package

[shaziaruybal]

When installing the SIMPLEGEN package, it failed because of following error message:

In addition: Warning message:
package ‘dust’ is not available for this version of R

To install dust from source, followed the instructions on github.com/mrc-ide/dust:

# install.packages("drat") # -- if you don't have drat installed
drat:::add("ncov-ic")
install.packages("dust")

Then installed SIMPLEGEN via devtools as usual:
devtools::install_github("mrc-ide/SIMPLEGEN")