Update the API for the Savon 2 interface

The Savon 2 API is nice but pretty different from Savon 1. Luckily this
simple client required only simple changes.

http://savonrb.com/version2/changes.html
All new VCR cassettes because Savon 2 makes new requests
Bump version now that we use Savon 2

No front end changes, just an update to the internal API used to talk to
the periodic table data.
Merge branch 'update-for-savon-2'