Update contributing.md

Author: dead-claudia

docs/contributing.md

@@ -12,7 +12,7 @@ Contribution guide for Mithril.js
 - [How do I embed live previews in docs?](#how-do-i-embed-live-previews-in-docs?)
 - [Why do tests mock the browser APIs?](#why-do-tests-mock-the-browser-apis?)
 - [Why does Mithril.js use its own testing framework and not Mocha/Jasmine/Tape?](#why-does-mithriljs-use-its-own-testing-framework-and-not-mochajasminetape?)
-- [Why doesn't the Mithril.js codebase use ES6 via Babel or Bublé? Would a PR to upgrade be welcome?](#why-doesn't-the-mithril-codebase-use-es6-via-babel-or-bublé?-would-a-pr-to-upgrade-be-welcome?)
+- [Why doesn't the Mithril.js codebase use ES6 via Babel or Bublé? Would a PR to upgrade be welcome?](#why-doesn't-the-mithriljs-codebase-use-es6-via-babel-or-bublé?-would-a-pr-to-upgrade-be-welcome?)
 - [Why doesn't the Mithril.js codebase use trailing semi-colons? Would a PR to add them be welcome?](#why-doesn't-the-mithriljs-codebase-use-trailing-semi-colons?-would-a-pr-to-add-them-be-welcome?)
 - [What should I know in advance when attempting a performance related contribution?](#what-should-i-know-in-advance-when-attempting-a-performance-related-contribution?)
 - [Do you all accept donations?](#do-you-all-accept-donations?)