Fixes small typo in SASS syntax for switch label text padding

removed a comma which causes the emcalc function to render the $switch-label-side-padding as "0" in the output CSS file

Example of current switch CSS with padding typo/error here:
http://foundation.zurb.com/docs/components/switch.html
Merge pull request #3431 from HoldenCreative/patch-1

Fixes small typo in SASS syntax for switch label text padding