Add "repository" field to avoid warning message

package.json

@@ -9,6 +9,7 @@
   },
   "author": "Drew Winget <scipioaffricanus@gmail.com> (https://aeschylus.net/)",
   "license": "MIT",
+  "repository": "https://github.com/ProjectMirador/research-and-demos/tree/master/minimal_redux_poc",
   "dependencies": {
     "jest": "21.2.1",
     "redux": "3.7.2"