Fix `rand_real` to return random number `[0,1)` not `[0,1]`.

mrbgems/mruby-random/src/random.c

@@ -90,7 +90,7 @@ static double
 rand_real(rand_state *t)
 {
   uint32_t x = rand_uint32(t);
-  return x*(1.0/4294967295.0);
+  return x*(1.0/4294967296.0);
 }
 #endif