Travis CI is no longer used (#718)

* refactor: remove broken link in `README.md`

* Delete .travis.yml

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Co-authored-by: Christian Clauss <cclauss@me.com>

README.md

@@ -2,7 +2,6 @@
 
 #### @mapbox/node-pre-gyp makes it easy to publish and install Node.js C++ addons from binaries
 
-[![Build Status](https://travis-ci.com/mapbox/node-pre-gyp.svg?branch=master)](https://travis-ci.com/mapbox/node-pre-gyp)
 [![Build status](https://ci.appveyor.com/api/projects/status/3nxewb425y83c0gv)](https://ci.appveyor.com/project/Mapbox/node-pre-gyp)
 
 `@mapbox/node-pre-gyp` stands between [npm](https://github.com/npm/npm) and [node-gyp](https://github.com/Tootallnate/node-gyp) and offers a cross-platform method of binary deployment.