Fix error assertion's message

This fixes the error message to reflect the changes described in [Defining Relationships in Models](https://github.com/emberjs/data/blob/master/TRANSITION.md#defining-relationships-in-models).
Fix incorrect documentation for isError.

If the server returns a validation error, then isError is not set to true.
Fix validation comments for

- Api docs included comments on failing client-side validation
- DS.model doesn't have client side validation
- Only code that sets errors and changes  is a result
  of an invalid response from server
[DOC beta] Clarify adapter settings with ActiveModel::Serializers
allow saving records from invalid state

tests by @alexspeller
Add a better transform example
[DOC] Fix docs for method signature of extractSingle, extractArray
Fixes a typo in the documentation of the serializeAttribute method of json_serializer.js
Merge pull request #1887 from pixelhandler/active-model-adapter-docs-settings

[DOC] Clarify adapter settings with ActiveModel::Serializers
Merge pull request #1885 from pixelhandler/validation-comments-correction

[DOC] Fix validation comments for DS.Model#isValid
Specify language as Node.js on Travis CI

Without `language` section, Travis CI detects Ruby as build language:
* https://travis-ci.org/emberjs/data/builds/24150621#L18
Use npm-scripts to run test

* https://www.npmjs.org/doc/misc/npm-scripts.html
Merge pull request #1906 from tricknotes/install-grunt-on-travis

Fix failing test on Travis CI.
Use `package.json` as gem version
Fix to update ember-data version

Now, ember-data is versioned as 1.0.0-beta.8+canary.
Cleanup scripts

* Remove old script `bin/cached-bundle`
* Fix to update comment for `bin/cached-npm`
Merge pull request #1907 from tricknotes/cleanup-scripts

Cleanup scripts
Add `repository` field to package.json

To suppress warning from npm:
```
npm WARN package.json ember-data@1.0.0-beta.7+canary No repository field.
```
Add `license` field to package.json
Merge pull request #1908 from tricknotes/add-repository-field-to-package.json

Add `repository` field to package.json