message: Add downloads badge
diff: # ts-jest
  +[![NPM downloads](https://img.shields.io/npm/dm/ts-jest.svg?style=flat)](https://npmjs.org/package/ts-jest)
  [![Build Status for node v7](https://travis-badges.herokuapp.com/repos/kulshekhar/ts-jest/branches/master?job=0)](https://travis-ci.org/kulshekhar/ts-jest)
  [![Build Status for node v6](https://travis-badges.herokuapp.com/repos/kulshekhar/ts-jest/branches/master?job=1)](https://travis-ci.org/kulshekhar/ts-jest)
  [![Build Status for node v4](https://travis-badges.herokuapp.com/repos/kulshekhar/ts-jest/branches/master?job=2)](https://travis-ci.org/kulshekhar/ts-jest)
  