Use migration command to construct log message (#254)

lib/capistrano/tasks/migrations.rake

@@ -10,7 +10,7 @@ namespace :deploy do
       if conditionally_migrate && test(:diff, "-qr #{release_path}/db #{current_path}/db")
         info '[deploy:migrate] Skip `deploy:migrate` (nothing changed in db)'
       else
-        info '[deploy:migrate] Run `rake db:migrate`'
+        info "[deploy:migrate] Run `rake #{fetch(:migration_command)}`"
         # NOTE: We access instance variable since the accessor was only added recently. Once capistrano-rails depends on rake 11+, we can revert the following line
         invoke :'deploy:migrating' unless Rake::Task[:'deploy:migrating'].instance_variable_get(:@already_invoked)
       end