[libcalamaresui] Update SPDX identifiers.

Update ImageRegistry.cpp

src/libcalamaresui/utils/ImageRegistry.cpp

@@ -1,6 +1,6 @@
 /* === This file is part of Calamares - <https://github.com/calamares> ===
  *
- *   SPDX-License-Identifier: GPLv3+
+ *   SPDX-License-Identifier: GPL-3.0-or-later
  *   License-Filename: LICENSES/GPLv3+-ImageRegistry
  *
  *   Copyright 2019, Adriaan de Groot <groot@kde.org>

src/libcalamaresui/utils/ImageRegistry.h

@@ -1,6 +1,6 @@
 /* === This file is part of Calamares - <https://github.com/calamares> ===
  *
- *   SPDX-License-Identifier: GPLv3+
+ *   SPDX-License-Identifier: GPL-3.0-or-later
  *   License-Filename: LICENSES/GPLv3+-ImageRegistry
  *
  *   Copyright 2019, Adriaan de Groot <groot@kde.org>