Updated logo for NSIS installer

**Before**

![before](https://cloud.githubusercontent.com/assets/6345473/3218599/83705d88-efec-11e3-902c-39b0ccdfa609.PNG)

**After**

![after](https://cloud.githubusercontent.com/assets/6345473/3218600/8370bd50-efec-11e3-9bd3-99a7eaeacc56.PNG)