Fix serialization results in the documentation.

[nathanhammond]

I believe that this is a mistake in the description, but I'm unfamiliar enough with Ember Data to be unsure. :)

[bmac]

I believe career is correct in this case because the attribute is remapped by the {key: 'career'} option: https://github.com/emberjs/data/pull/3004/files#diff-cce3ad76c2e3801ed1a94bf5276dbbbbR81.

Here is a simple jsbin that demonstrates the example in the docs:
http://emberjs.jsbin.com/lisuyahoma/1/edit?html,css,js,console

It does appear that the firstName and lastName are missing from the serialized example. If you would like to change this pr to add those I would be happy to merge it.

[nathanhammond]

I read it as a deserialize instead of a serialize. :) Patch modified to include additional details.

[bmac]

Thanks.