Ensured it is never less than 0

Author: dvilchez

coffee/react-countdown-clock.coffee

@@ -62,7 +62,7 @@ module.exports = React.createClass
     setTimeout ( =>
       duration = Date.now() - start
       @setState
-        seconds: @state.seconds - duration / 1000
+        seconds: Math.max(0,@state.seconds - duration / 1000)
       @_tick() unless @state.seconds <= 0
     ), 30