Local font source is not recognized as valid

[Rarst]

Only font faces having src: url() are treated as valid, so src: local() ones would always be considered invalid and dropped, even if they are detected as critical fonts.

@font-face {
  font-family: "Alegreya-fallback";
  size-adjust: 101%;
  src: local("Times New Roman");
}

critters/packages/critters/src/index.js

Lines 568 to 587 in a590c05

	src = (decl.value.match(/url\s*\(\s*(['"]?)(.+?)\1\s*\)/) || [])[2];
	} else if (decl.prop === 'font-family') {
	family = decl.value;
	}
	}
	if (src && shouldPreloadFonts && preloadedFonts.indexOf(src) === -1) {
	preloadedFonts.push(src);
	const preload = document.createElement('link');
	preload.setAttribute('rel', 'preload');
	preload.setAttribute('as', 'font');
	preload.setAttribute('crossorigin', 'anonymous');
	preload.setAttribute('href', src.trim());
	document.head.appendChild(preload);
	}
	// if we're missing info, if the font is unused, or if critical font inlining is disabled, remove the rule:
	if (
	!family ||
	!src ||

Related #112