Fix for failing component unmount test

Test failure detected while running jasmine specs with latest Bacon.js (0.7.30)

Testing jasmine specs via PhantomJS
 BaconMixin
   #eventStream
     - returns the stream for that defined name......√
     - returns always the same event stream......√
     - defines a function property with the name of the stream......√
     - that defined function can be used as event handler, and pushes to the stream......√
     - removes subscribers when the component unmounts......×
       TypeError: 'undefined' is not a function (evaluating 'stream.hasSubscribers()') in /project/node_modules/react-bacon/tmp/specs.js (line 22246) (1)