use stoppable fork for node 4.x compatibility

Author: mblackstock

package.json

@@ -17,7 +17,7 @@
     "should": "^8.4.0",
     "sinon": "1.17.7",
     "supertest": "3.0.0",
-    "stoppable": "^1.0.5",
+    "stoppable": "boneskull/stoppable#boneskull-patch-1",
     "when": "3.7.8"
   },
   "peerDependencies": {