Don't setup pusher if we don't have key

That way we don't need to even fire anything pusher related when running
tests

assets/scripts/app/app.coffee

@@ -10,7 +10,7 @@ unless window.TravisApplication
       @store.loadMany(Travis.Sponsor, Travis.SPONSORS)
 
       @slider = new Travis.Slider()
-      @pusher = new Travis.Pusher(Travis.config.pusher_key)
+      @pusher = new Travis.Pusher(Travis.config.pusher_key) if Travis.config.pusher_key
       @tailing = new Travis.Tailing()
 
       @set('auth', Travis.Auth.create(app: this, endpoint: Travis.config.api_endpoint))

assets/scripts/app/models/job.coffee

@@ -87,11 +87,13 @@ require 'travis/model'
   subscribe: ->
     return if @get('subscribed')
     @set('subscribed', true)
+    if Travis.pusher
       Travis.pusher.subscribe "job-#{@get('id')}"
 
   unsubscribe: ->
     return unless @get('subscribed')
     @set('subscribed', false)
+    if Travis.pusher
       Travis.pusher.unsubscribe "job-#{@get('id')}"
 
   onStateChange: (->