The fs sensor now rounds the resulting number with 2 digits

On my system the free space on hd had many digits after the decimal point.
![before](https://cloud.githubusercontent.com/assets/61795/4100292/da64b6d4-308d-11e4-9617-27d1b0a27e48.png)

Now it shows only two digits.
![after](https://cloud.githubusercontent.com/assets/61795/4100291/da638e3a-308d-11e4-8983-960203e3451d.png)