Update project.clj

I was getting the following error when starting the app:

'Could not find artifact org.clojure:core.async:jar:0.1.0-SNAPSHOT in clojars (https://clojars.org/repo/)
This could be due to a typo in :dependencies or network issues.
If you are behind a proxy, try setting the 'http_proxy' environment variable.'

This change resolves that.