Fix mismatch due to steam returning an https uri now

[Arie]

Steam started returning a https uri in the openid response, causing a mismatch with the expected uri. This PR just changes it to expect an https uri.

[btalbot]

Since the change was unannounced (AFAIK) and there's a non-zero chance that steam might change it back on a whim, I'd prefer a more robust solution to allow http or https. Something like https://github.com/iJJi/omniauth-steam/commit/29cb118de793065798d4ff3298bf74fc8b1e9afd

[edit] and https://github.com/iJJi/omniauth-steam/commit/368049fb44481a8d1de45a84fd1f6448900cac9d with regexp anchors

[fbluemel]

+1 to a robust solution, but ...

• that dot in the regex should be escaped
• Regexp#match? is Ruby 2.4 -- since the gemspec does not declare a min version, it might be better to just use good old Regexp#match ... but I admit I may be biased because I'm too lazy to upgrade from 2.3

[MisterTakaashi]

I merged all your ideas in #31, I hope it's ok for you @Arie too 👍

[Arie]

It's way better than my PR :)

[btalbot]

Thanks for making a better patch. I had to be out of town for a few days and could not get back to this. I like #31 too.