dmm: change params to match those in the 3 eq nile example in the dmm submodule

tests/nile.mod

@@ -26,7 +26,7 @@ S2.calibration(process=2, regime=1) = 1;
 S2.calibration(process=2, regime=2) = 2;
 
 //P2.prior(shape=dirichlet,mean=3,variance=3,params=[16,2]);
-P1.prior(shape=dirichlet,mean=3,variance=3,params=[18,2]);
+P1.prior(shape=dirichlet,mean=3,variance=3,params=[8 4 4 1]);
 
 // we need to add Dirichlet shape and params field the number of params must be equal to number of regimes in multinomial declaration
 Ve.prior(shape=inv_gamma,mean=6e4,stdev=6,interval=[0,5e4]);