dockerimg: detect more dockerfiles

diff --git a/dockerimg/dockerimg.go b/dockerimg/dockerimg.go
index cd0906f..da3ccbb 100644
--- a/dockerimg/dockerimg.go
+++ b/dockerimg/dockerimg.go
@@ -901,7 +901,7 @@
 			return filepath.SkipDir
 		}
 		name := strings.ToLower(info.Name())
-		if name == "dockerfile" || strings.HasPrefix(name, "dockerfile.") {
+		if name == "dockerfile" || strings.HasPrefix(name, "dockerfile.") || strings.HasSuffix(name, ".dockerfile") {
 			res = append(res, path)
 		}
 		return nil