Replace request with got

[avaly]

This PR replaces request with a lighter-weight got and adds a unit test for loading of images from URLs.

Before:

$ yarn install --production
// node_modules: 6901208 bytes, 727 files

After:

$ yarn install --production
// node_modules: 2227162 bytes, 260 files

[yahoocla]

Thank you for submitting this pull request, however I do not see a valid CLA on file for you. Before we can merge this request please visit https://yahoocla.herokuapp.com/ and agree to the terms. Thanks! 😄

[coveralls]

Coverage decreased (-71.0%) to 8.012% when pulling 8f952ee on avaly:refactor/replace-request-with-got into 63f11c6 on yahoo:master.