Fix logDone message for TestCopySingleFileToExistDir

Signed-off-by: Alexandr Morozov <lk4d4@docker.com>

integration-cli/docker_cli_build_test.go

@@ -322,7 +322,7 @@ func TestCopySingleFileToExistDir(t *testing.T) {
 
 	deleteImages("testcopyimg")
 
-	logDone("build - add single file to existing dir")
+	logDone("build - copy single file to existing dir")
 }
 
 func TestCopySingleFileToNonExistDir(t *testing.T) {