Use hardcoded value for PropType secret (facebook#7194)

Rename secret!

Author: aweary

src/isomorphic/classic/types/ReactPropTypesSecret.js

@@ -13,6 +13,6 @@
 'use strict';
 
 
-const ReactPropTypesSecret = '__REACT_PROP_TYPES_SECRET__' + Math.random().toString();
+const ReactPropTypesSecret = 'SECRET_DO_NOT_PASS_THIS_OR_YOU_WILL_BE_FIRED';
 
 module.exports = ReactPropTypesSecret;