Update Machine.java

mutants/mutant-2/swen90006/machine/Machine.java

@@ -106,7 +106,7 @@ public class Machine
 
   private int parseReg(String s) throws InvalidInstructionException
   {
-    if (s.length() < 2){
+    if (s.length() < 3){
       throw new InvalidInstructionException();
     }
     if (s.charAt(0) != 'r'){