[Matlab/Examples] Don't call non-existent methods

The current simulation time is a property of the reactor network, not the
individual reactors.

samples/matlab/reactor1.m

@@ -53,7 +53,7 @@ t0 = cputime;
 for n = 1:100
   t = t + dt;
   advance(network, t);
-  tim(n) = time(r);
+  tim(n) = time(network);
   temp(n) = temperature(r);  
   x(n,1:3) = moleFraction(gas,{'OH','H','H2'});
 end

samples/matlab/reactor2.m

@@ -31,7 +31,7 @@ t0 = cputime;
 for n = 1:100
   t = t + dt;
   advance(network, t);
-  tim(n) = time(r);
+  tim(n) = time(network);
   temp(n) = temperature(r);  
   x(n,1:3) = moleFraction(gas,{'OH','H','H2'});
 end