Created by: MartijnCuppens
There are a lot of redundant brackets in the scss, this PR cleans this up a bit. I still left the brackets on some places if it increased the readability of the code like here: https://github.com/twbs/bootstrap/blob/e9ec5e73929a46852abf9c7d4e5fc03d50f76d3c/scss/_popover.scss#L134