Accept https urls (feature request)

[benwhalley]

For example, this fails:

SASxport::read.xport('https://wwwn.cdc.gov/Nchs/Nnyfs/Y_DEMO.XPT')

But this doesn't

SASxport::read.xport('http://wwwn.cdc.gov/Nchs/Nnyfs/Y_DEMO.XPT')

[gwarnes-mdsol]

I confirmed this issue.