Remove optionalDependencies. It's not needed.

ghengeveld · ghengeveld · commit 9fd4b0027a31 · 2019-07-31T10:18:39.000+02:00
diff --git a/packages/react-async/package.json b/packages/react-async/package.json
@@ -26,9 +26,6 @@
   "peerDependencies": {
     "react": ">=16.3.1"
   },
-  "optionalDependencies": {
-    "prop-types": ">=15.5.7"
-  },
   "@pika/pack": {
     "pipeline": [
       [
