update vrouter (fix pop issues with modal sheets)

Recent versions of vrouter properly support the showModal* functions,
which solves the issues with the android back button popping the chat
view instead of closing a user sheet or image view. Fixes #426.

pubspec.lock

@@ -1214,7 +1214,7 @@ packages:
       name: vrouter
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.2+5"
+    version: "1.1.4+11"
   watcher:
     dependency: transitive
     description:
@@ -1265,5 +1265,5 @@ packages:
     source: hosted
     version: "3.1.0"
 sdks:
-  dart: ">=2.12.1 <3.0.0"
+  dart: ">=2.13.0 <3.0.0"
   flutter: ">=2.0.2"

pubspec.yaml

@@ -69,7 +69,7 @@ dependencies:
   unifiedpush: ^1.0.2
   universal_html: ^2.0.8
   url_launcher: ^6.0.3
-  vrouter: ^1.1.2+5
+  vrouter: ^1.1.4+11
 
 dev_dependencies:
   dapackages: ^1.6.0