feat: add a11y contribution type (#223)

* feat: add a11y contribution type

* Fix missing comma in `contribution-types.js`

Author: phacks

src/util/contribution-types.js

@@ -3,6 +3,10 @@ const repo = require('../repo')
 
 const defaultTypes = function(repoType) {
   return {
+    a11y: {
+      symbol: '️️️️♿️',
+      description: 'Accessibility',
+    },
     blog: {
       symbol: '📝',
       description: 'Blogposts',