Add API token to fix CircleCI badge in README

Apparently [1] you need this even for public projects despite what the CircleCI
docs say [2].

[1]: https://discuss.circleci.com/t/build-status-badge-not-showing-on-github/35803/4
[2]: https://circleci.com/docs/2.0/status-badges/#generating-a-status-badge

README.md

@@ -1,4 +1,4 @@
-## Mocha [![CircleCI status of freerange/mocha](https://circleci.com/gh/freerange/mocha.svg?style=shield)](https://app.circleci.com/pipelines/github/freerange/mocha) [![Gem Version](https://badge.fury.io/rb/mocha.svg)](http://badge.fury.io/rb/mocha) [![SemVer](https://api.dependabot.com/badges/compatibility_score?dependency-name=mocha&package-manager=bundler&version-scheme=semver)](https://dependabot.com/compatibility-score.html?dependency-name=mocha&package-manager=bundler&version-scheme=semver)
+## Mocha [![CircleCI status of freerange/mocha](https://circleci.com/gh/freerange/mocha.svg?style=shield&circle-token=bc1f6576c77da43ec58badde9273fa4eb1d7f53a)](https://app.circleci.com/pipelines/github/freerange/mocha) [![Gem Version](https://badge.fury.io/rb/mocha.svg)](http://badge.fury.io/rb/mocha) [![SemVer](https://api.dependabot.com/badges/compatibility_score?dependency-name=mocha&package-manager=bundler&version-scheme=semver)](https://dependabot.com/compatibility-score.html?dependency-name=mocha&package-manager=bundler&version-scheme=semver)
 
 ### Description