Issues in installation of dev version of ggmap library in R

General
2

Thanks for the nice and crisp explanation,
However,
I am getting some errors on trying to install the dev version of ggmap.
on executing

devtools::install_github("dkahle/ggmap")

I get this error:


> devtools::install_github("dkahle/ggmap")
Error in curl::curl_fetch_memory(url, handle = h) : 
  schannel: next InitializeSecurityContext failed: SEC_E_UNTRUSTED_ROOT (0x80090325) - The certificate chain was issued by an authority that is not trusted.

Pls note , I am running Rstudio with R3.5.2 on a windows 7 64 bit machine
Any suggestions would be helpful.
Thanks.
Dush