[MPL] Fix copyright years.

MaterialLib/MPL/Properties/RelativePermeability/RelPermBrooksCorey.cpp

@@ -5,7 +5,7 @@
  * \brief
  *
  * \copyright
- * Copyright (c) 2012-2018, OpenGeoSys Community (http://www.opengeosys.org)
+ * Copyright (c) 2012-2020, OpenGeoSys Community (http://www.opengeosys.org)
  *            Distributed under a Modified BSD License.
  *              See accompanying file LICENSE.txt or
  *              http://www.opengeosys.org/project/license

MaterialLib/MPL/Properties/RelativePermeability/RelPermLiakopoulos.cpp

@@ -4,7 +4,7 @@
  * \brief
  *
  * \copyright
- * Copyright (c) 2012-2018, OpenGeoSys Community (http://www.opengeosys.org)
+ * Copyright (c) 2012-2020, OpenGeoSys Community (http://www.opengeosys.org)
  *            Distributed under a Modified BSD License.
  *              See accompanying file LICENSE.txt or
  *              http://www.opengeosys.org/project/license