Improve accuracy of reference result in a few test cases.

prism-tests/functionality/verify/ctmcs/rewards/ctmc_rewards.sm.props

@@ -11,7 +11,7 @@ R{"a"}=? [ C<=10 ];
 // RESULT: 12.11429
 R{"a"}=? [ C<=100 ];
 
-// RESULT: 12.11429
+// RESULT: 12.114285714285716
 R{"a"}=? [ C ];
 
 // RESULT: Infinity

prism-tests/functionality/verify/ptas/reach/zeroconf.nm.props

@@ -16,7 +16,7 @@ Pmax=? [ F s=2 & ip=L ];
 const int T = 150;
 
 // Maximum probability of configuring IP address incorrectly by time T
-// RESULT (T=100): 6.51605e-4
-// RESULT (T=150): 0.001072525539875
-// RESULT (T=200): 0.001221541934004246875
+// RESULT (T=100): 130321/200000000
+// RESULT (T=150): 8580204319/8000000000000
+// RESULT (T=200): 390893418881359/320000000000000000
 "deadline": Pmax=? [ F<=T s=2 & ip=2 ];