Fixed bug which caused buttons to have a height of 33px instead of 34px

Hi there,

I had a strange bug today in my chrome browser which caused bootstrap buttons to have a height of 33px instead of the usual 34px. After some research, I found out that its a know issue and can be fixed by increasing the the precision of the sass compiler.

Cheers,
Peer

Found cause and fix here: 
thomas-mcdonald/bootstrap-sass#409
gruntjs/grunt-contrib-compass#113