docs: update link to trademark policy (npm#389)

The current link to the trademark policy https://www.npmjs.com/policies/trademark#the-npm-trademark-policy is dead (I get 404 response page). I have updated it to point to the trademark section of the disputes page here https://docs.npmjs.com/policies/disputes#trademarks (hopefully this is acceptable).

content/packages-and-modules/contributing-packages-to-the-registry/package-name-guidelines.mdx

@@ -16,5 +16,5 @@ Additionally, when choosing a name for an [**unscoped** package][create-unscoped
 
 
 [policies]: https://www.npmjs.com/policies
-[npm-trademark]: https://www.npmjs.com/policies/trademark#the-npm-trademark-policy
+[npm-trademark]: https://docs.npmjs.com/policies/disputes#trademarks
 [create-unscoped]: creating-and-publishing-unscoped-public-packages