Make parser optional

types/sanitize-html/index.d.ts

@@ -5,6 +5,7 @@
 //                 BehindTheMath <https://github.com/BehindTheMath>
 //                 Rinze de Laat <https://github.com/biermeester>
 //                 Will Gibson <https://github.com/WillGibson>
+//                 A penguin <https://github.com/sirMerr>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 import {Options} from "htmlparser2";
@@ -54,7 +55,7 @@ declare namespace sanitize {
     nonTextTags?: string[];
     selfClosing?: string[];
     transformTags?: { [tagName: string]: string | Transformer };
-    parser: Options;
+    parser?: Options;
   }