Use new name in BUCK Implementation-URL

Change-Id: I4d99a8a7653dd518287fe3cd359e51cddb8c7b42

BUCK

diff --git a/BUCK b/BUCK
index 8e99cda..714abaf 100644
--- a/BUCK
+++ b/BUCK
@@ -5,7 +5,7 @@
   manifest_entries = [
     'Gerrit-PluginName: avatars-external',
     'Implementation-Title: External Avatar plugin',
-    'Implementation-URL: https://gerrit-review.googlesource.com/#/admin/projects/plugins/avatars/external',
+    'Implementation-URL: https://gerrit-review.googlesource.com/#/admin/projects/plugins/avatars-external',
     'Gerrit-AvatarProvider: com.googlesource.gerrit.plugins.avatars.external.ExternalUrlAvatarProvider',
   ],
 )