Update License Year (WordPress#13145)

Aurorum · ntwb · commit 6262b603bb5b · 2019-01-01T20:52:47.000+11:00
Minor change, but as countries start heading into 2019 within the next few hours, it's probably worth updating the License year now. 😄
diff --git a/LICENSE.md b/LICENSE.md
@@ -1,6 +1,6 @@
 ### WordPress - Web publishing software
 
-    Copyright 2011-2018 by the contributors
+    Copyright 2011-2019 by the contributors
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
