chore: small typo Wil[l] (#3216)

Minor spelling issue.

src/marked.ts

@@ -30,7 +30,7 @@ export function marked(src: string, options: MarkedOptions & { async: true }): P
  *
  * @param src String of markdown source to be compiled
  * @param options Optional hash of options
- * @return String of compiled HTML. Wil be a Promise of string if async is set to true by any extensions.
+ * @return String of compiled HTML. Will be a Promise of string if async is set to true by any extensions.
  */
 export function marked(src: string, options?: MarkedOptions): string | Promise<string>;
 export function marked(src: string, opt?: MarkedOptions): string | Promise<string> {