Fix first-child/last-child matching.

@@ -237,16 +237,19 @@ const compileMatcher = (ast: AST, selector: string): MatcherProducer => {
             }
           case 'first-child':
             return (context, node, parent, i, debug) => {
-              return parent?.children.findFirst(child => child.type === ELEMENT_NODE) === node
+              const children = findChildren(context, parent, 'ELEMENT', filterChildElementsMatcher)
+              return children[ 0 ] == node
             }
           case 'last-child':
             return (context, node, parent, i, debug) => {
-              return parent?.children.findLast(child => child.type === ELEMENT_NODE) === node
+              const children = findChildren(context, parent, 'ELEMENT', filterChildElementsMatcher)
+              return children[ children.length - 1 ] == node
             }
           case 'only-child':
             return (context, node, parent, i, debug) => {
               // TODO: This can break-early after it finds the second element
-              return findChildren(context, parent, 'ELEMENT', filterChildElementsMatcher).length === 1
+              const children = findChildren(context, parent, 'ELEMENT', filterChildElementsMatcher)
+              return children.length === 1
             }
           // case 'nth-of-type':
           // case 'nth-last-of-type':