message: docs(Readme): Add link to dependency status
diff: [![CircleCI](https://circleci.com/gh/ideal-postcodes/postcodes.io/tree/master.svg?style=svg)](https://circleci.com/gh/ideal-postcodes/postcodes.io/tree/master)
  [![Coverage Status](https://coveralls.io/repos/github/ideal-postcodes/postcodes.io/badge.svg?branch=master)](https://coveralls.io/github/ideal-postcodes/postcodes.io?branch=master)
  -![Dependency Status](https://david-dm.org/ideal-postcodes/postcodes.io.svg)
  +[![Dependency Status](https://david-dm.org/ideal-postcodes/postcodes.io.svg)](https://david-dm.org/ideal-postcodes/postcodes.io)
  Query for UK postcodes and geolocations over HTTP.
  