Add repository field to package.json

This allows NPM to link back to the repository
from the package page at <https://www.npmjs.com/package/@uphold/validator.js\>

Author: waldyrious

package.json

@@ -5,6 +5,7 @@
   "main": "index.js",
   "author": "Uphold",
   "license": "MIT",
+  "repository": "uphold/uphold-validator.js",
   "scripts": {
     "changelog": "uphold-scripts changelog $npm_package_version",
     "lint": "uphold-scripts lint",