Upgrade to Flutter 1.21.0-9.2.pre (#584)

diff --git a/.travis.yml b/.travis.yml
index 3fe8380..776136a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,8 +4,7 @@
 dart:
   # Keep this value aligned with min SDK value in pubspec.yaml and FROM line of Dockerfile
   - "2.9.2"
-  # 2.10 is currently breaking dart services. Tracking bug: https://github.com/dart-lang/dart-pad/issues/1616
-  # - beta
+  - beta
 
 # Use Ubuntu 18.04 (Bionic Beaver) 
 # https://docs.travis-ci.com/user/reference/overview/#virtualization-environments
diff --git a/flutter b/flutter
index 916c3ac..81a45ec 160000
--- a/flutter
+++ b/flutter
@@ -1 +1 @@
-Subproject commit 916c3ac648aa0498a70f32b5fc4f6c51447628e3
+Subproject commit 81a45ec2e5f80fa71d5135f1702ce540558b416d