Bump tinymce from 6.7.1 to 6.7.3 in /src/Umbraco.Web.UI.Client

Bumps [tinymce](https://github.com/tinymce/tinymce/tree/HEAD/modules/tinymce) from 6.7.1 to 6.7.3.
- [Changelog](https://github.com/tinymce/tinymce/blob/develop/modules/tinymce/CHANGELOG.md)
- [Commits](https://github.com/tinymce/tinymce/commits/6.7.3/modules/tinymce)

---
updated-dependencies:
- dependency-name: tinymce
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

src/Umbraco.Web.UI.Client/package.json

@@ -51,7 +51,7 @@
     "ng-file-upload": "12.2.13",
     "nouislider": "15.7.1",
     "spectrum-colorpicker2": "2.0.10",
-    "tinymce": "6.5.1",
+    "tinymce": "6.7.3",
     "typeahead.js": "0.11.1",
     "underscore": "1.13.6",
     "wicg-inert": "3.1.2"