Update to Flutter 1.21.0-9.1.pre (#580)

diff --git a/.travis.yml b/.travis.yml
index 4bac4bf..d0688fc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,7 +4,8 @@
 dart:
   # Keep this value aligned with min SDK value in pubspec.yaml and FROM line of Dockerfile
   - "2.9.1"
-  - beta
+  # 2.10 is currently breaking dart services. Tracking bug: https://github.com/dart-lang/dart-pad/issues/1616
+  # - beta
 
 # Use Ubuntu 18.04 (Bionic Beaver) 
 # https://docs.travis-ci.com/user/reference/overview/#virtualization-environments
diff --git a/Dockerfile b/Dockerfile
index a0f844d..0953b60 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -6,7 +6,7 @@
 # To retrieve this value, please run the following in your closest shell:
 #
 # $ (cd flutter && git rev-parse HEAD)
-ARG FLUTTER_COMMIT=916c3ac648aa0498a70f32b5fc4f6c51447628e3
+ARG FLUTTER_COMMIT=be9bc8cb3942bda5d8ef4e44b44616c470625e18
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.
diff --git a/cloud_run.Dockerfile b/cloud_run.Dockerfile
index 1bc8011..a898a69 100644
--- a/cloud_run.Dockerfile
+++ b/cloud_run.Dockerfile
@@ -6,7 +6,7 @@
 # To retrieve this value, please run the following in your closest shell:
 #
 # $ (cd flutter && git rev-parse HEAD)
-ARG FLUTTER_COMMIT=916c3ac648aa0498a70f32b5fc4f6c51447628e3
+ARG FLUTTER_COMMIT=be9bc8cb3942bda5d8ef4e44b44616c470625e18
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.
diff --git a/flutter b/flutter
index 916c3ac..be9bc8c 160000
--- a/flutter
+++ b/flutter
@@ -1 +1 @@
-Subproject commit 916c3ac648aa0498a70f32b5fc4f6c51447628e3
+Subproject commit be9bc8cb3942bda5d8ef4e44b44616c470625e18