Bump version back so that np can be the one to bump the version.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@polymer/polymer",
-  "version": "3.5.2",
+  "version": "3.5.1",
   "description": "The Polymer library makes it easy to create your own web components. Give your element some markup and properties, and then use it on a site. Polymer provides features like dynamic templates and data binding to reduce the amount of boilerplate you need to write",
   "main": "polymer-element.js",
   "module": "polymer-element.js",