Fixed issue that allows it to work with Boostrap library

Hi There :)

I was using the plugin with Bootstrap and was causing an issue whereby the line height for li's was set by Bootstrap, rather than the flipclock.

![image](https://f.cloud.github.com/assets/6059732/2263562/6240bb48-9e67-11e3-85f8-c9304368e40c.png)

Added a line which defines the li as having the line height, overwriting any changes from bootstrap.