Fix duplicate route to setup/leak-canary-plugin

Summary:
Noticed this when building the site. Shame it only warns and doesn't fail the build.
Just fixing it while I'm here.

{F479009268}

Reviewed By: nikoant

Differential Revision: D26911725

fbshipit-source-id: 6440a4b8aee4a6bc053ae771a3b148fd70ffc298

website/sidebars.js

@@ -88,6 +88,7 @@ module.exports = {
       'setup/sandbox-plugin',
       'setup/shared-preferences-plugin',
       'setup/leak-canary-plugin',
+      'setup/leak-canary-2-plugin',
       'setup/crash-reporter-plugin',
     ],
     Advanced: ['custom-ports', 'stetho'],