In error, the first letter is low-case letter

Signed-off-by: YuPengZTE <yu.peng36@zte.com.cn>

distribution/pull_v2.go

@@ -810,7 +810,7 @@ func fixManifestLayers(m *schema1.Manifest) error {
 
 	if imgs[len(imgs)-1].Parent != "" && runtime.GOOS != "windows" {
 		// Windows base layer can point to a base layer parent that is not in manifest.
-		return errors.New("Invalid parent ID in the base layer of the image.")
+		return errors.New("invalid parent ID in the base layer of the image")
 	}
 
 	// check general duplicates to error instead of a deadlock

distribution/pull_v2_test.go

@@ -80,7 +80,7 @@ func TestFixManifestLayersBaseLayerParent(t *testing.T) {
 		},
 	}
 
-	if err := fixManifestLayers(&duplicateLayerManifest); err == nil || !strings.Contains(err.Error(), "Invalid parent ID in the base layer of the image.") {
+	if err := fixManifestLayers(&duplicateLayerManifest); err == nil || !strings.Contains(err.Error(), "invalid parent ID in the base layer of the image") {
 		t.Fatalf("expected an invalid parent ID error from fixManifestLayers")
 	}
 }