Add build phase to .travis.yml to publish to npm

[martijnthe]

• Add build phase to .travis.yml to publish to npm
• Add npm badge to README.md

[martijnthe]

Putting this here so I don't loose it.

Hi Martijn,

$ travis encrypt TOKEN -r jerryscript-project/jerryscript-debugger-ts
Please add the following to your .travis.yml file:

  secure: "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"

Cheers,
Akos