USWDS: Breadcrumb - Changes negative margin from shorthand to left/right

[mahoneycm]

Resolves #4240

Description

Uses @mejiaj 's solution to fix negative margin overlap error by changing margin: units($theme-focus-width) * -1; to

margin-left: units($theme-focus-width) * -1;
margin-right: units($theme-focus-width) * -1;

Additional information

Before

After

Before you hit Submit, make sure you’ve done whichever of these applies to you:

• [ x ] Follow the 18F Front End Coding Style Guide and Accessibility Guide.
• [ x ] Run npm test and make sure the tests for the files you have changed have passed.
• Run your code through HTML_CodeSniffer and make sure it’s error free.
• [ x ] Title your pull request using this format: [Website] - [UI component]: Brief statement describing what this pull request solves.