Update year in license files

In last year's update (D48219) it was suggested that the release manager
might want to do this, so here we go.

llvm-svn: 351194
GitOrigin-RevId: eb60fbfdb43cb8583eda1e338b3489ddef332f10
diff --git a/LICENSE.TXT b/LICENSE.TXT
index 0134694..1c94ad5 100644
--- a/LICENSE.TXT
+++ b/LICENSE.TXT
@@ -14,7 +14,7 @@
 University of Illinois/NCSA
 Open Source License
 
-Copyright (c) 2009-2018 by the contributors listed in CREDITS.TXT
+Copyright (c) 2009-2019 by the contributors listed in CREDITS.TXT
 
 All rights reserved.