Update opn (facebook#3784)

Author: gaearon

packages/react-dev-utils/package.json

@@ -47,7 +47,7 @@
     "gzip-size": "3.0.0",
     "inquirer": "3.3.0",
     "is-root": "1.0.0",
-    "opn": "5.1.0",
+    "opn": "5.2.0",
     "react-error-overlay": "^3.0.0",
     "recursive-readdir": "2.2.1",
     "shell-quote": "1.6.1",