REL: update license year to 2019

Author: pavoljuhas

LICENSE.txt

@@ -11,7 +11,7 @@ the following paper in your publication:
     crystals, J. Phys.: Condens.  Matter 19, 335219 (2007)
 
 Copyright 2006-2007, Board of Trustees of Michigan State University,
-Copyright 2008-2016, Board of Trustees of Columbia University in the
+Copyright 2008-2019, Board of Trustees of Columbia University in the
 city of New York.  (Copyright holder indicated in each source file).
 
 For more information please visit the project web-page: