Update rxdart dependency to 0.24.0.

Author: pauldemarco

pubspec.yaml

@@ -15,7 +15,7 @@ dependencies:
     sdk: flutter
   convert: "^2.1.1"
   protobuf: "^1.0.1"
-  rxdart: ^0.23.1
+  rxdart: ^0.24.0
 
 dev_dependencies:
   flutter_test: