chore(code.angularjs.org): fix robots.txt

- allow all-versions-data.js in snapshot, which is used by docs.angularjs.org
- disallow access to folders like docs-0.9.2 etc which are used by early versions

Author: Narretz

scripts/code.angularjs.org-firebase/public/robots.txt

@@ -1,5 +1,6 @@
 User-agent: *
 
-Disallow: /*docs/
+Disallow: /*docs*/
 Disallow: /*i18n/
 Disallow: /*.zip$
+Allow: /snapshot/docs/js/all-versions-data.js