Remove useless quotes in font-stacks

Created by: ffoodd

• Matthias Bynens wrote about "unquote font family names in CSS" back in 2012;
• and went with a neat tool to check wheter your font-family name requires quotes or not;
• FWIW, StyleLint rule to check quotes in family names is set to where-recommended in our StyleLint config → PR #55 opened