Poke migration-management versions for 1.6.6

Author: jcflack

pljava/src/main/java/org/postgresql/pljava/internal/InstallHelper.java

@@ -991,6 +991,7 @@ void migrateFrom( SchemaVariant sv, Connection c, Statement s)
 		UNREL20040120  ("5e4131738cd095b7ff6367d64f809f6cec6a7ba7"),
 		EMPTY          (null);
 
+		static final SchemaVariant REL_1_6_6       = REL_1_6_0;
 		static final SchemaVariant REL_1_6_5       = REL_1_6_0;
 		static final SchemaVariant REL_1_6_4       = REL_1_6_0;
 		static final SchemaVariant REL_1_6_3       = REL_1_6_0;