twitteR, “Peer certificate cannot be authenticated

Question

> install_github("twitteR", username="geoffjentry")
Installing github repo twitteR/master from geoffjentry
Downloading master.zip from https://github.com/geoffjentry/twitteR/archive/master.zip
Error in function (type, msg, asError = TRUE)  : 
  Peer certificate cannot be authenticated with given CA certificates
> 
> sessionInfo()
R version 3.1.0 (2014-04-10)
Platform: x86_64-pc-linux-gnu (64-bit)