fix admin component generator namespace

Author: ccarruitero

admin/lib/generators/solidus_admin/install/templates/config/initializers/solidus_admin.rb.tt

@@ -37,4 +37,7 @@ SolidusAdmin::Config.configure do |config|
   #     }
   #   ]
   # }
+
+  # Define namespace for component generator
+  ::Rails::Generators.namespace = SolidusAdmin
 end