Update NewApplication.md

Dear, 

I believe I found a spot that needs to be changed in the document 

http://www.playframework.com/documentation/2.3.x/NewApplication

The document says that we should use the command 

Activator new $ my-first-app play-java 

But it seems that this template does not exist in the repository. I leave attached a screenshot with the error 

I think the correct template should look like this: 

http://typesafe.com/activator/template/play-java-preview