Parsl / parsl

With typeguard 2.3, loading parsl.monitoring.monitoring issues
this warning:

```
>>> import parsl.monitoring.monitoring
/home/benc/parsl/virtualenv-3.7/lib/python3.7/site-packages/typeguard.py:505: UserWarning: no type annotations present -- not typechecking parsl.monitoring.monitoring.MonitoringHub
  warn('no type annotations present -- not typechecking {}'.format(function_name(func)))
```

This commit forces a newer version which works.