Bump jquery from 3.3.1 to 3.4.0 in /default-assets-package

Bumps [jquery](https://github.com/jquery/jquery) from 3.3.1 to 3.4.0.
- [Release notes](https://github.com/jquery/jquery/releases)
- [Commits](jquery/jquery@3.3.1...3.4.0)

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

default-assets-package/package.json

@@ -26,7 +26,7 @@
     "grunt-contrib-copy": "^1.0.0",
     "grunt-contrib-less": "^2.0.0",
     "grunt-exec": "3.0.0",
-    "jquery": "^3.3.1",
+    "jquery": "^3.4.0",
     "load-grunt-tasks": "^4.0.0",
     "octicons": "4.4.0",
     "timeago": "1.6.4"