Improved Fritzing Icon

Before:
![fritzing_icon_old](https://cloud.githubusercontent.com/assets/7050624/5204429/c0dde9be-758f-11e4-81cd-21b4f70927c7.png)
After:
![fritzing_icon_new](https://cloud.githubusercontent.com/assets/7050624/5204431/c8a7b92c-758f-11e4-9f69-f7211046e96e.png)