fix(api-builder): fix path to upgrade/static library (#3450)

This invalid path was causing the static upgrade
library to be missed from the API documentation.

tools/api-builder/angular.io-package/index.js

@@ -70,7 +70,7 @@ module.exports = new Package('angular.io', [basePackage, targetPackage, cheatshe
     'router/index.ts',
     'router/testing/index.ts',
     'upgrade/index.ts',
-    'upgrade/static.ts'
+    'upgrade/static/index.ts'
   ];
   readTypeScriptModules.hidePrivateMembers = true;