fix: correct link to Mocha website (#152)

Author: jawn

Diff for: api/test.md

@@ -9,5 +9,5 @@
 
 This is the test suite that we use to test Chai during development. Use it to confirm
 that Chai will function correctly in your browser environment (`should` does
-not work in IE9). These tests are powered by the awesome [Mocha](http://visionmedia.github.com/mocha/)
+not work in IE9). These tests are powered by the awesome [Mocha](https://mochajs.org/)
 test framework.