iotiel-sgrun simulator trace function is broken (never ported to python 3)

See:

```
(env) PS C:\Arch\core\coretools\iotilesensorgraph> iotile-sgrun.exe C:\Users\TimBurke\Desktop\test.sgf -s 'run_time 1 minute' -t C:\Users\TimBurke\Desktop\trace.txt
Traceback (most recent call last):
File "C:\Arch\core\workspace\env\Scripts\iotile-sgrun-script.py", line 11, in
load_entry_point('iotile-sensorgraph', 'console_scripts', 'iotile-sgrun')()
File "c:\arch\core\coretools\iotilesensorgraph\iotile\sg\scripts\iotile_sgrun.py", line 194, in main
sim.trace.save(args.trace)
File "c:\arch\core\coretools\iotilesensorgraph\iotile\sg\sim\trace.py", line 52, in save
json.dump(out, outfile, indent=4)
File "C:\Python38\lib\json\__init__.py", line 180, in dump
fp.write(chunk)
TypeError: a bytes-like object is required, not 'str'
```

The `test.sgf` was (but it shouldn't matter):
```
every 1 second
{
call 0x8000 on controller => unbuffered 2;
call 0x8002 on controller => unbuffered 2;
}

on value(unbuffered 2) == 5
{
call 0x8001 on slot 1 => output 1;
}
```