pgsql: Fix insufficiently-portable regression test case.

Fix insufficiently-portable regression test case.

Some of the buildfarm members are evidently miserly enough of stack space
to pass the originally-committed form of this test.  Increase the
requirement 10X to hopefully ensure that it fails as-expected everywhere.

Security: CVE-2015-5289

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/57b02827f3c086695e82358d7466b0168c64d3b9

Modified Files
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src/test/regress/expected/json.out   |    4 ++--
src/test/regress/expected/json_1.out |    4 ++--
src/test/regress/sql/json.sql        |    4 ++--
3 files changed, 6 insertions(+), 6 deletions(-)