Update change log and pubspec for release 0.7.3 (#84)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a21ebc..0135f25 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## Unreleased
+## 0.7.3 - 2017-07-05
 
 ### gRPC support
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 5c59ddb..2cb5c64 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: protoc_plugin
-version: 0.7.2
+version: 0.7.3
 author: Dart Team <misc@dartlang.org>
 description: Protoc compiler plugin to generate Dart code
 homepage: https://github.com/dart-lang/dart-protoc-plugin