[Fix #671] Increase `nrepl-sync-request-timeout' to 30 seconds

When jvm starts for the first time, the very first sync request `(str *ns*)` timeouts. 

As `nrepl-send-sync-request` doesn't have an explicit treatment of timeout error (`keyboard-quit`). Thus the cause of the issue was not easy to spot. In  #729 I have fixed the error reporting in this and a couple of other places.