Add "prop-types" to dependencies of "react-test-renderer" (#11340)

Author: gaearon

package.json

@@ -16,7 +16,8 @@
   "homepage": "https://reactjs.org/",
   "dependencies": {
     "fbjs": "^0.8.16",
-    "object-assign": "^4.1.1"
+    "object-assign": "^4.1.1",
+    "prop-types": "^15.6.0"
   },
   "peerDependencies": {
     "react": "^16.0.0"