change rep image as a gif

Author: cric96

imgs/example-rep.gif

@@ -303,7 +303,7 @@ rep(0)(x => x+1)
 
 counts how many rounds each device has executed. Indeed, the first time the `rep` expression is evaluated at some device, `x` is bound to `0`, and the expression evaluates to `0+1=1`; the next round on the same device, `x` is bound to `1` (i.e., to the value of the expression in the previous round) and the expression evaluates to `1+1=2`; and so on. It is still -- in general -- a non-uniform field since the update phase and frequency of the devices may vary both between devices and across time for a given device. The following figure shows a snapshot of a field generated by the above expression.
 
-![Dynamically evolving field with rep.](/imgs/example-rep.png){:.centered}
+![Dynamically evolving field with rep.](/imgs/example-rep.gif){:.centered}
 
 Notice that if we assume a bulk synchronous execution model, the output of the above expression would be a **non-constant but uniform field**.