Doc: correct nitpicky mistakes in array_position/array_positions examples.

Daniel Gustafsson and Erik Rijkers, per report from nick@cleaton

Discussion: https://postgr.es/m/159275646273.679.16940709892308114570@wrigleys.postgresql.org

doc/src/sgml/array.sgml

@@ -669,14 +669,16 @@ SELECT * FROM sal_emp WHERE pay_by_quarter && ARRAY[10000];
 
 <programlisting>
 SELECT array_position(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon');
- array_positions
+ array_position
------------------
+----------------
               2
+(1 row)
 
 SELECT array_positions(ARRAY[1, 4, 3, 1, 3, 4, 2, 1], 1);
  array_positions
 -----------------
  {1,4,8}
+(1 row)
 </programlisting>
  </para>