fix JER SET OF invalid output

[mtfurlan]

JER set of has invalid output right now.

$ cat test.asn 
Module DEFINITIONS::=BEGIN T::=SET OF INTEGER END

$ cat thing.xml 
<?xml version="1.0" encoding="UTF-8"?>
<T>
  <INTEGER>10</INTEGER>
  <INTEGER>12</INTEGER>
  <INTEGER>-2</INTEGER>
  <INTEGER>8</INTEGER>
</T>

$ ./converter-example -ixer thing.xml -p T -ojer > out.json
$ cat out.json
{
"T":
    "INTEGER"10
    "INTEGER"12
    "INTEGER"-2
    "INTEGER"8
}