Use protocol-relative src for connect.facebook.net

I'm not sure how I ended up on the HTTPS version of iNat, but when I did I noticed this error in the JavaScript console:

[blocked] The page at https://www.inaturalist.org/projects/biodiversity-of-martha-s-vineyard ran insecure content from http://connect.facebook.net/en_US/all.js.

Switching the protocol-relative URLs for the src should do the trick.

*Note*: I'm not yet set up to run the app, but this change is pretty cut and dry.