Inject linting into CI pipeline

[roll]

Overview

If I've got it right we don't have something like pretest: npm review in package.json to have linting as a part of test run.

Tasks

• [ ] setup linting for travis
• [ ] make sure it passes

[roll]

@dumyan please also take a look on this. I've pushed it on of first things - https://github.com/frictionlessdata/datapackage-js/milestone/1 - it will be easier to start linting while there are no so much code