Format code with gofmt

This commit fixes the style issues introduced in ac05190 according to the output
from gofmt.

Details: https://deepsource.io/gh/romanornr/autodealer/transform/39bbe652-4ffe-4e2b-a50c-b6ed2e7e52df/

singleton/dealer_test.go

@@ -15,4 +15,4 @@ func TestGetDealerInstance(t *testing.T) {
 		webserver.GetDealerInstance()
 	}()
 	wg.Wait()
-}
+}