Update copyright for 2018

Backpatch-through: certain files through 9.3

COPYRIGHT

 PostgreSQL Database Management System
 (formerly known as Postgres, then as Postgres95)
 
-Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
+Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 
 Portions Copyright (c) 1994, The Regents of the University of California
 

doc/src/sgml/legal.sgml

 <!-- doc/src/sgml/legal.sgml -->
 
-<date>2017</date>
+<date>2018</date>
 
 <copyright>
- <year>1996-2017</year>
+ <year>1996-2018</year>
  <holder>The PostgreSQL Global Development Group</holder>
 </copyright>
 
@@ -11,7 +11,7 @@
  <title>Legal Notice</title>
 
  <para>
-  <productname>PostgreSQL</productname> is Copyright &copy; 1996-2017
+  <productname>PostgreSQL</productname> is Copyright &copy; 1996-2018
   by the PostgreSQL Global Development Group.
  </para>