THRIFT-4106: fix errors concurrency_test was identifying
Client: C++

This closes #1343
diff --git a/build/docker/debian-stretch/Dockerfile b/build/docker/debian-stretch/Dockerfile
index 70309fb..503eecd 100644
--- a/build/docker/debian-stretch/Dockerfile
+++ b/build/docker/debian-stretch/Dockerfile
@@ -56,6 +56,7 @@
       gdb \
       ninja-build \
       pkg-config \
+      valgrind \
       vim