rCharts包安装不了，求大神指点


> require(devtools)
> install_github('rCharts', 'ramnathv')
Installation failed: Problem with the SSL CA cert (path? access rights?)
Warning message:
Username parameter is deprecated. Please use ramnathv/rCharts
> install_github('ramnathv/rCharts ')
Installation failed: Problem with the SSL CA cert (path? access rights?)