Dart 2.13.4 (#741)

diff --git a/cloud_run.Dockerfile b/cloud_run.Dockerfile
index 68f0a27..ea31bb2 100644
--- a/cloud_run.Dockerfile
+++ b/cloud_run.Dockerfile
@@ -1,4 +1,4 @@
-FROM google/dart:2.13.3
+FROM google/dart:2.13.4
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.
diff --git a/cloud_run_null_safety.Dockerfile b/cloud_run_null_safety.Dockerfile
index 0e70a69..1b6036a 100644
--- a/cloud_run_null_safety.Dockerfile
+++ b/cloud_run_null_safety.Dockerfile
@@ -1,4 +1,4 @@
-FROM google/dart:2.13.3
+FROM google/dart:2.13.4
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.