Bump backbone from 1.3.3 to 1.4.0

Bumps [backbone](https://github.com/jashkenas/backbone) from 1.3.3 to 1.4.0.
- [Release notes](https://github.com/jashkenas/backbone/releases)
- [Commits](https://github.com/jashkenas/backbone/compare/1.3.3...1.4.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

package.json

@@ -25,7 +25,7 @@
     "@chenfengyuan/vue-qrcode": "^1.0.0",
     "Select2": "git+https://github.com/select2/select2.git#3.4.8",
     "autosize": "^4.0.2",
-    "backbone": "^1.3.3",
+    "backbone": "^1.4.0",
     "blueimp-md5": "^2.10.0",
     "bootstrap": "^4.3.1",
     "clipboard": "^2.0.4",