Bump mobx from 2.1.1 to 2.1.3 in /zxscanner

Bumps [mobx](https://github.com/mobxjs/mobx.dart) from 2.1.1 to 2.1.3.
- [Release notes](https://github.com/mobxjs/mobx.dart/releases)
- [Commits](https://github.com/mobxjs/mobx.dart/compare/mobx-2.1.1...mobx-2.1.3)

---
updated-dependencies:
- dependency-name: mobx
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

zxscanner/pubspec.lock

@@ -531,7 +531,7 @@ packages:
       name: mobx
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.1"
+    version: "2.1.3"
   mobx_codegen:
     dependency: "direct dev"
     description:

zxscanner/pubspec.yaml

@@ -25,7 +25,7 @@ dependencies:
   image: ^3.2.2
   image_picker: ^0.8.5
   intl: ^0.17.0
-  mobx: ^2.1.1
+  mobx: ^2.1.3
   path_provider: ^2.0.11
   share_plus: ^5.0.0
   shared_preferences: ^2.0.15