Switch from homepage to repository in pubspec (#173)

diff --git a/pubspec.yaml b/pubspec.yaml
index 4d250f4..f6b91d3 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -5,7 +5,7 @@
 name: usage
 version: 4.1.0-dev
 description: A Google Analytics wrapper for command-line, web, and Flutter apps.
-homepage: https://github.com/dart-lang/usage
+repository: https://github.com/dart-lang/usage
 
 environment:
   sdk: '>=2.15.0 <3.0.0'