Added assertion for updateLink

Added an assertion for string type. Since you could also pass objects
to `updateLink` (which would always result in false in the next if
statement) containing a link. This PR notifies creators of serializers
so they always use a string when handling links.

Added test for links with type other than string
Removed a duplicate line.
Added test case for push link with null value
Remove unnecessary `Function#call`
Merge pull request #2387 from tricknotes/remove-unnecessary-call

Remove unnecessary `Function#call`
Make dependencies clearer.

This is mostly just for easier discovery/understanding for passers by
looking at the `bower.json` in the root of the repo. The actual
`bower.json` that we put in components/ember-data is correct already.
Merge pull request #2390 from rwjblue/deps

Make dependencies clearer.
Refactored InvalidError handling into a serializer concern.
Merge pull request #2392 from ahacking/serialization-for-invalid-error

Refactored InvalidError handling into a serializer concern.
Merge pull request #2354 from steffenbrem/update-links-assert-fix

Added assertion for updateLink
Fixing an issue when grouping requests could result in URL longer than configured length.