Build: Upgrade from marked@2.x to marked@4.x

Various CVEs are fixed in the latest 4.x release:
https://github.com/markedjs/marked/security

Upgrade notes:
* https://github.com/markedjs/marked/releases/tag/v3.0.0
* https://github.com/markedjs/marked/releases/tag/v4.0.0
* https://github.com/markedjs/marked/blob/v4.0.19/docs/USING_PRO.md

Author: Krinkle

lib/util.js

@@ -34,7 +34,7 @@ function parseMarkdown( src, options ) {
 		}
 
 		// Store original text and create an id for linking
-		var parsedText = marked( item.text );
+		var parsedText = marked.marked( item.text );
 		parsedText = parsedText.substring( 3, parsedText.length - 5 );
 		item.tocText = parsedText.replace( /<[^>]+>/g, "" );
 		item.tocId = item.tocText

package-lock.json

@@ -26,7 +26,7 @@
     "grunt-wordpress": "^2.1.3",
     "he": "^1.2.0",
     "highlight.js": "^10.7.2",
-    "marked": "^2.0.3",
+    "marked": "^4.0.0",
     "spawnback": "^1.0.1",
     "which": "^2.0.2",
     "wordpress": "^1.4.1"