Fix type to allow undefined for props

Author: wooorm

Diff for: lib/core.js

@@ -42,7 +42,7 @@ export function core(schema, defaultTagName, caseSensitive) {
      * @type {{
      *   (): Root
      *   (selector: null|undefined, ...children: HChild[]): Root
-     *   (selector: string, properties: HProperties, ...children: HChild[]): Element
+     *   (selector: string, properties?: HProperties, ...children: HChild[]): Element
      *   (selector: string, ...children: HChild[]): Element
      * }}
      */