Add explicit phosphor dependencies

package.json

@@ -8,6 +8,8 @@
   "typings": "lib/index.d.ts",
   "dependencies": {
     "@jupyterlab/services": "^0.38.0",
+    "@phosphor/application": "^0.1.2",
+    "@phosphor/widgets": "^0.1.3",
     "ansi_up": "^1.3.0",
     "backbone": "^1.2.0",
     "codemirror": "^5.20.2",