Update CODEOWNERS for pkgs/watcher. (#2179)

Author: davidmorgan

.github/CODEOWNERS

@@ -43,6 +43,6 @@ pkgs/term_glyph                 @dart-lang/dart-bat
 pkgs/test_reflective_loader     @scheglov
 pkgs/timing                     @dart-lang/dart-bat
 pkgs/unified_analytics          @bkonyi @dart-lang/dash-developer-services
-pkgs/watcher                    @dart-lang/dart-ecosystem-team
+pkgs/watcher                    @davidmorgan @dart-lang/dart-model-team
 pkgs/yaml                       @dart-lang/dart-pub-team
 pkgs/yaml_edit                  @dart-lang/dart-pub-team