Cannot get memory used report

```
uWSGI = "2.0.19.1"
uwsgitop = "^0.11.0"
```

and uwsgi.ini config:

```
memory-report   = true
```

but the rss value always 0, 

> "rss":0,
> "vsz":0,
> "uss":0,
> "pss":0,

someone occured ?
