chore(package): Update author URL & maintainers

`mat.io` doesn't have any contents and might have expired. Added myself as a maintainer.

package.json

@@ -2,7 +2,10 @@
   "name": "cheerio",
   "version": "1.0.0-rc.9",
   "description": "Tiny, fast, and elegant implementation of core jQuery designed specifically for the server",
-  "author": "Matt Mueller <mattmuelle@gmail.com> (mat.io)",
+  "author": "Matt Mueller <mattmuelle@gmail.com>",
+  "maintainers": [
+    "Felix Boehm <me@feedic.com>"
+  ],
   "funding": "https://github.com/cheeriojs/cheerio?sponsor=1",
   "license": "MIT",
   "keywords": [