[skip ci] Fails, I mean Rails, 4.2. Round 1 of n.

See the (long) second comment on Issue #147.

Skip CI because we still haven't fixed all the problems yet.

RSpec: 664 examples, 2 failures
RuboCop: 180 files inspected, no offenses detected
[Close #147] Now clean with Rails 4.2.

See the discussion in Issue #147. This last change prevents `JSON.dump`
from attempting to serialise the `errors` attribute of the entity. This
was just fine prior to Rails 4.2; apparently, no longer. :disappointed:

RSpec: 664 examples, 2 failures
RuboCop: 180 files inspected, no offenses detected
Merge pull request #148 from jdickey/issue-147

[Close #147] Rails now upgraded to 4.2.0.
Housekeeping: Updated Gem dependencies.

RSpec: 664 examples, 2 failures
RuboCop: 180 files inspected, no offenses detected