Present perfect continuous matches plural

Summary:
This isn't a big deal, just saw it and submitted a PR.

https://www.englishforums.com/English/HasBeenVSHaveBeen/zzbx/post.htm
Closes https://github.com/facebook/react-native/pull/9508

Differential Revision: D3749803

fbshipit-source-id: c234ae102af055ecabcedae2e483441e26284516

local-cli/rnpm/link/src/link.js

@@ -85,7 +85,7 @@ const linkAssets = (project, assets) => {
     copyAssetsAndroid(assets, project.android.assetsPath);
   }
 
-  log.info(`Assets has been successfully linked to your project`);
+  log.info(`Assets have been successfully linked to your project`);
 };
 
 /**