Update repository url

Currently, the package.json points to the wrong repository, so it's pretty hard to find this package. 😄

Author: danmactough

packages/babel-preset-mapbox/package.json

@@ -14,7 +14,7 @@
   },
   "repository": {
     "type": "git",
-    "url": "git+https://github.com/mapbox/babel-preset-mapbox.git"
+    "url": "git+https://github.com/mapbox/underreact.git"
   },
   "author": "Mapbox",
   "contributors": [