Fix "Develop extensions" link in developer.chrome.com navbar JSON.

chrome/common/extensions/docs/templates/json/chrome_sidenav.json

 [
   {
     "title": "Devtools",
     "items": [
       {
         "title": "Learn Basics",
         "href": "/devtools",
         "items": [
           {
             "title": "Overview",
@@ skipping 547 matching lines @@
           {
             "title": "Getting Started Tutorial",
             "href": "/extensions/getstarted"
           },
           {
             "title": "Samples",
             "href": "/extensions/samples"
           },
           {
             "title": "Develop Extensions",
-            "href": "/extensions/tut_migration_to_manifest_v2",
+            "href": "/extensions",
             "items": [
               {
                 "title": "Accessibility",
                 "href": "/extensions/a11y"
               },
               {
                 "title": "Content Security Policy",
                 "href": "/extensions/contentSecurityPolicy"
               },
               {
@@ skipping 468 matching lines @@
                 "title": "Articles",
                 "href": "/webstore/articles"
               }
             ]
           }
         ]
       }
     ]
   }
 ]