move whatwg-fetch to deps

dev_mode/package.json

@@ -54,7 +54,8 @@
     "@jupyterlab/ui-components-extension": "~1.1.0-alpha.2",
     "@jupyterlab/vdom-extension": "~1.1.0-alpha.2",
     "@jupyterlab/vega4-extension": "~1.1.0-alpha.2",
-    "@jupyterlab/vega5-extension": "~1.1.0-alpha.2"
+    "@jupyterlab/vega5-extension": "~1.1.0-alpha.2",
+    "whatwg-fetch": "^3.0.0"
   },
   "devDependencies": {
     "@jupyterlab/buildutils": "^1.1.0-alpha.2",
@@ -82,7 +83,6 @@
     "webpack-bundle-analyzer": "^3.4.1",
     "webpack-cli": "^3.3.0",
     "webpack-merge": "^4.2.1",
-    "whatwg-fetch": "^3.0.0",
     "yarn-deduplicate": "^1.1.1"
   },
   "resolutions": {