Fix continue in switch statement

The "continue" statement in a switch case doesn't work as it should. The following code yields this result:

    var i = 0;
    while (i++ < 3) {
      switch (i) {
        case 1:
          print("one");
          continue;
        case 2:
          print("two");
          continue;
        default:
          print("default");
          continue;
      }
    }

    one
    two
    default
    two
    default
    default

It seems the SwitchStatement class was ignoring CompletionType.Type.CONTINUE. With this change I get the expected result:

    one
    two
    default