Update Voice Design Guide link

The link is updated to https://developer.amazon.com/en-US/alexa/alexa-haus from https://developer.amazon.com/designing-for-voice/

Author: aszk

README.md

@@ -35,7 +35,7 @@ Additional Resources
 
 ### Tutorials & Guides
 
--  [Voice Design Guide](https://developer.amazon.com/designing-for-voice/) -
+-  [Voice Design Guide](https://developer.amazon.com/en-US/alexa/alexa-haus) -
    A great resource for learning conversational and voice user interface design.
 
 ### Documentation