Update rxdart

Author: rrousselGit

packages/custom_lint/pubspec.yaml

@@ -23,7 +23,7 @@ dependencies:
   path: ^1.8.0
   pub_semver: ^2.1.1
   pubspec_parse: ^1.2.0
-  rxdart: ^0.27.7
+  rxdart: ^0.28.0
   uuid: ">=3.0.6 <5.0.0"
   yaml: ^3.1.1