Switch to https

This version responds to the following notice from the EIA:

Notice: As of February 11st, 2022 The API now only responds to HTTPS. Insecure (HTTP) web protocols are no longer supported.

Changes:

• Changed requests to EIA API from http to https.
• New depends on httr package.

Thanks to @MoreCoffee12 for identifying the issue, and providing code fixes.