Small changes to code - rvm file change + https

Hi there.  I've made a few small changes to my branch of the code (building up to add support for new programs) that I wanted to offer back to you.

RVM has moved on in the 2 years since you last changed missingnprpodcasts; it recommends changing to .ruby_version instead of .rvm; this patch has that change.

I've also changed from http to https for accessing NPR; there seems to be no good reason to not access it securely IMHO.