Update Flutter to 1.20.0-7.4.pre (#571)

diff --git a/Dockerfile b/Dockerfile
index c9226d5..9c77258 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=e606910f28be51c8151f6169072afe3b3a8b3c5e
+ARG FLUTTER_COMMIT=916c3ac648aa0498a70f32b5fc4f6c51447628e3
 
 # 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 600f558..a44d40d 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=e606910f28be51c8151f6169072afe3b3a8b3c5e
+ARG FLUTTER_COMMIT=916c3ac648aa0498a70f32b5fc4f6c51447628e3
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.
diff --git a/flutter b/flutter
index e606910..916c3ac 160000
--- a/flutter
+++ b/flutter
@@ -1 +1 @@
-Subproject commit e606910f28be51c8151f6169072afe3b3a8b3c5e
+Subproject commit 916c3ac648aa0498a70f32b5fc4f6c51447628e3
diff --git a/pubspec.lock b/pubspec.lock
index 0671517..e8f75c2 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -98,14 +98,14 @@
       name: build_runner
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.10.0"
+    version: "1.10.1"
   build_runner_core:
     dependency: transitive
     description:
       name: build_runner_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "5.2.0"
+    version: "6.0.1"
   built_collection:
     dependency: transitive
     description:
@@ -189,7 +189,7 @@
       name: csslib
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.16.1"
+    version: "0.16.2"
   dart_style:
     dependency: transitive
     description: