Documentation - fix links on README.md and typo on CONTRIBUTING.md

[anneswanson]

On the README.md, correct 3 links.

• For more in depth information on development check out our contributors readme should point to: https://github.com/DigitalRiver/react-atlas/blob/master/docs/CONTRIBUTING.md

• Contributing Guidelines link should point to: https://github.com/DigitalRiver/react-atlas/blob/master/docs/CONTRIBUTING.md

• Contributor Code of Conduct should point to: https://github.com/DigitalRiver/react-atlas/blob/master/docs/CODE_OF_CONDUCT.md

On CONTRIBUTING.md fix typo: Write tests & code in ES6 goodness :-) un the test suite: npm run test

should instead be:

Write tests & code in ES6 goodness :-) run the test suite: npm run test

[anneswanson]

Pull request: https://github.com/DigitalRiver/react-atlas/pull/975