Correct psql documentation example

An example in the psql documentation had an incorrect field name from
what the command actually produced.

Pointed out by Fabien COELHO

Back-patch to 9.6 where the example was added.

Discussion: https://postgr.es/m/alpine.DEB.2.20.1611291349400.19314@lancre

doc/src/sgml/ref/psql-ref.sgml

@@ -4172,7 +4172,7 @@ second | four
   with the <command>\crosstabview</command> command:
 <programlisting>
 testdb=&gt; <userinput>SELECT first, second, first &gt; 2 AS gt2 FROM my_table;</userinput>
- first | second | ge2 
+ first | second | gt2 
 -------+--------+-----
      1 | one    | f
      2 | two    | f