THRIFT-5285 Update http package + update to dart 2 + stylistic changes
Client: Dart
Patch: aaronstgeorge-wf

This closes #2251
diff --git a/build/docker/ubuntu-xenial/Dockerfile b/build/docker/ubuntu-xenial/Dockerfile
index 20ee117..e3aff74 100644
--- a/build/docker/ubuntu-xenial/Dockerfile
+++ b/build/docker/ubuntu-xenial/Dockerfile
@@ -114,7 +114,7 @@
     mv openssl-1.1.6-1.0.1g/C/* /usr/include/dmd/druntime/import/C/ && \
     rm -rf openssl-1.1.6-1.0.1g
 
-ENV DART_VERSION 2.0.0-1
+ENV DART_VERSION 2.7.2-1
 RUN apt-get install -y --no-install-recommends \
 `# Dart dependencies` \
       dart=$DART_VERSION