Updated promises icon

![promise_icon](https://f.cloud.github.com/assets/497659/1951450/7fceb48a-817f-11e3-91e6-a3bd4e33bebf.png)

![promise_icon](https://f.cloud.github.com/assets/497659/1951465/10fbaada-8180-11e3-8078-c9f8708d43c4.png)