Fixing index page documentation's Develop drop down menu links

In the local build documentation page, Develop drop down menu links (Tutorial, Developer Guide & API reference) was pointing to the production url (docs.angularjs.org). 
This fixes the hardcoded links & pointing to the appropriate urls in the localhost build doc. 

Hopefully, it works fine in the production url as well. If not, we might need to do some location.hostname prefixing using javascript.