Do not use random() for the distribution to test CDB_Stats functions

Fixes #144

test/CDB_StatsTest.sql

@@ -2,15 +2,12 @@
 -- http://mathworld.wolfram.com/UniformDistribution.html
 set client_min_messages to ERROR;
 
-With dist As (
-  SELECT random()::numeric As val
-  FROM generate_series(1,50000) t
+WITH dist AS (
+  SELECT generate_series(0,10000)::numeric / 10000.0 i
 )
-
-SELECT 
-  -- does random dist values match within 1% of known values
-  abs(CDB_Kurtosis(array_agg(val)) + 1.20) < 1e-2 As kurtosis,
-  abs(CDB_Skewness(array_agg(val)) - 0) < 1e-2 As skewness
+SELECT
+  abs(CDB_Kurtosis(array_agg(i)) + 1.2) < 1e-3 AS kurtosis,
+  abs(CDB_Skewness(array_agg(i))) < 1e-3 AS skewness
 FROM dist;
 
 set client_min_messages to NOTICE;