pgsql: Docs: fix erroneous claim about max byte length of GB18030.

Docs: fix erroneous claim about max byte length of GB18030.

This encoding has characters up to 4 bytes long, not 2.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/cde3e743cdc6317711913c0cee8a8c56f49ea87c

Modified Files
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doc/src/sgml/charset.sgml |    2 +-
1 file changed, 1 insertion(+), 1 deletion(-)