Spacing issues in color rules

[spalger]

Kibana version: master
Elasticsearch version: master
Server OS version: dev
Original install method (e.g. download page, yum, from source, etc.): source
Description of the problem including expected versus actual behavior:

The spacing between rules in the color field formatter look broken

Steps to reproduce:

1. Edit a numeric field
2. Set the formatter to "Color"
3. Add a few rules

[cjcenizal]

@spalger Unassigning myself (no time right now)