Add myself as maintainer

Well, since I'm currently the maintainer of CodiMD, I should maybe
mentioned in the package.json, just in case someone is willing to
contact me about it.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

package.json

@@ -147,6 +147,10 @@
     {
       "name": "Max Wu",
       "email": "jackymaxj@gmail.com"
+    },
+    {
+      "name": "Christoph (Sheogorath) Kern",
+      "email": "codimd@sheogorath.shivering-isles.com"
     }
   ],
   "repository": {