fix(prefix): make use of -- as a prefix standard

[diego-codes]

It adds an extra - to the prefixing of class name so it is consistent with Carbon's prefixing standards. This is so that the $prefix value is respected in the building of sass code for Carbon users.

[diego-codes]

Sadly we can’t make that update on the IBM grid package because it would conflict with Carbon’s prefix variable bx.

The class names themselves need to be updated to include -- in them like the rest of Carbon’s Sass. That way a consuming developer can declare their own $prefix and generate class names that are consistent all across.

[seejamescode]

In that case, it sounds like the real fix is changing the prefix variable in Carbon right before the grid is imported and then switching the variable back right afterwards. Would that work?

Otherwise, a major change we need to do is prefix the prefix variable in Gridish.