Update lots of gems.

This updates all gems except excon, faraday and webmock.
Initially, I updated those gems, too, but they caused
test failures.  I'll be updating those separately.
Update Faraday.

Faraday 0.8.6 includes a User-Agent request header by default.
Remove failing faraday cukes.

Faraday has some additional headers (see bf9b312a1f6dc2da048d935c2925de85ac1f95c1) that
do not match what is in the VCR cassette for this example. We've got this covered with
some specs already, and there's not much documentation value here to working around it,
so it's simplest just to remove the faraday scenarios.
Merge pull request #273 from vcr/upgrade_gems

Update lots of gems.