Switch from homepage to repository in pubspec (#32)

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index 4f8cb93..585fa61 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,7 +1,7 @@
 name: clock
 version: 1.1.0
 description: A fakeable wrapper for dart:core clock APIs
-homepage: https://github.com/dart-lang/clock
+repository: https://github.com/dart-lang/clock
 
 environment:
   sdk: ">=2.12.0-0 <3.0.0"