Update sanitize-html tests to cover with & without parser options (#28682)

See https://github.com/punkave/sanitize-html/issues/248#issuecomment-418859354 for context

Re: "Increase the version number in the header if appropriate." My brain is not able to figure out what that means.

- [x] Use a meaningful title for the pull request. Include the name of the package modified.
- [x] Test the change in your own code. (Compile and run.)
- [x] Add or edit tests to reflect the change. (Run with `npm test`.)
- [x] Follow the advice from the [readme](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/README.md#make-a-pull-request).
- [x] Avoid [common mistakes](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/README.md#common-mistakes).
- [x] Run `npm run lint package-name` (or `tsc` if no `tslint.json` is present).

If changing an existing definition:
- [x] Provide a URL to documentation or source code which provides context for the suggested changes: <<url here>>
- [ ] Increase the version number in the header if appropriate.
- [ ] If you are making substantial changes, consider adding a `tslint.json` containing `{ "extends": "dtslint/dt.json" }`.

types/sanitize-html/sanitize-html-tests.ts

@@ -29,12 +29,15 @@ let options: sanitize.IOptions = {
   allowedSchemesByTag: {
     'a': ['http', 'https']
   },
-  allowProtocolRelative: false,
-  parser: {
-    decodeEntities: true
-  }
+  allowProtocolRelative: false
 };
 
 let unsafe = '<div><script>alert("hello");</script></div>';
 
 let safe = sanitize(unsafe, options);
+
+options.parser = {
+    decodeEntities: true
+};
+
+safe = sanitize(unsafe, options);