Remove redundant brackets

[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:

bootstrap/scss/_popover.scss

Line 134 in e9ec5e7

border-width: ($popover-arrow-width / 2) 0 ($popover-arrow-width / 2) $popover-arrow-height;

[XhmikosR]

I don't think there's a rule for this, right? In stylelint-scss.

[MartijnCuppens]

@XhmikosR, no there isn't at the moment. My gut feeling tells me that'll also be a hard one to implement.

[XhmikosR]

LGTM AFAIK, but let's wait to hear from @mdo too

[mdo]

I'm fine to do either way here—having the parentheses helped me with readability and consistency across the project. Obviously a stylistic thing, so if folks don't want them, I'm fine with it. Would be also nice to have a linter for it though as @XhmikosR was suggesting.

[XhmikosR]

My main concern here is that if we can't automate the check, it's moot.

And having the extra brackets is a personal choice. I'm not against it, except for the cases it makes the expression more clear, but unless we can automate it, we'll just have to keep an eye for it manually, which is something not reliable.

[MartijnCuppens]

We're actually quite inconsistent with this, for example these calculations don't use brackets:

bootstrap/scss/_variables.scss

Lines 296 to 301 in 0a55c7a

	$h1-font-size: $font-size-base * 2.5 !default;
	$h2-font-size: $font-size-base * 2 !default;
	$h3-font-size: $font-size-base * 1.75 !default;
	$h4-font-size: $font-size-base * 1.5 !default;
	$h5-font-size: $font-size-base * 1.25 !default;
	$h6-font-size: $font-size-base !default;

bootstrap/scss/_variables.scss

Line 487 in 0a55c7a

$input-height-border: $input-border-width * 2 !default;

bootstrap/scss/_button-group.scss

Lines 70 to 71 in 0a55c7a

	padding-right: $btn-padding-x * .75;
	padding-left: $btn-padding-x * .75;

My main concern here is that if we can't automate the check, it's moot.

There are other things we always need to check ourself like the leading and trailing whitelines of titles in markdown files. I don't really like the idea that you can use whatever style you like here. Linting it would definitely be the best option, but I'm afraid this would be a plugin that is difficult to create, because you can have calc functions, scss variables, multiple value per property,...

[XhmikosR]

Let's go with it, just a 2-3 cases I think the brackets make it clearer.