Add a process for using semantic-release/github (or similar) to publish UMD file

[DamonOehlman]

The ability to access the UMD file for detect-browser is important, as it's something that folks in non-commonjs environments have expressed an interest in using. It is, however, unusual to commit generated files (as index.js is post the typescript conversion to the repo).

Using something like https://github.com/semantic-release/github and integrating it into the publishing flow would be an ideal way to point people to a useful UMD build of detect-browser.