fix: Added missing quotation mark in documentation

[Harmageddon]

Description

I noticed on https://foundation.zurb.com/sites/docs/sass.html that there was a piece of HTML code just before "Using Compiled CSS" that should not be there. Adding a quotation mark should fix this.

Types of changes

• Documentation
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to change)

Checklist (all required):

• I have read and follow the CONTRIBUTING document.
• There are no other pull request similar to this one.
• The pull request title is descriptive.
• The template is fully and correctly filled.
• The pull request targets the right branch (develop or develop-v...).
• My commits are correctly titled and contain all relevant information.
• My code follows the code style of this project.
• I have updated the documentation accordingly to my changes (if relevant).
• I have added tests to cover my changes (if relevant).
• All new and existing tests passed.

(didn't check the latest three points because it is a one-character HTML/MD change.

[ncoden]

Hi @Harmageddon, thank you for the pull request!