Fix multiline modifier descriptions on indent

[jho406]

Hi! I noticed there was support for multi-line modifier descriptions, but it breaks on anything >2 lines.

# Form Button

Your standard form button.

:hover    - Highlights when hovering.
:disabled - Dims the button when disabled.
.primary  - Indicates button is the primary action.
.smaller  - A smaller button
            for
            ants.

Styleguide 2.1.1.

That is unless you change it to this:

.smaller  - A smaller button
            for 
              ants.

This should fix the issue for nice indents.

[jho406]

Amended to increment instead. And made the test look a bit nicer.