add missing dependency

Author: bertho-zero

package.json

@@ -149,6 +149,7 @@
     "feathers-rest": "^1.7.3",
     "feathers-socketio": "^2.0.0",
     "http-proxy": "^1.16.2",
+    "is-promise": "^2.1.0",
     "js-cookie": "^2.1.3",
     "localforage": "^1.4.3",
     "lru-memoize": "^1.0.1",