Device_tracker nmap stopped working with error

so I had the device tracker with nmap working for maybe about a week now and all of the sudden it stopped working giving me this error

Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/device_tracker/__init__.py", line 694, in async_device_tracker_scan
    found_devices = yield from scanner.async_scan_devices()
  File "/usr/local/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/device_tracker/nmap_tracker.py", line 81, in scan_devices
    self._update_info()
  File "/usr/local/lib/python3.6/site-packages/homeassistant/components/device_tracker/nmap_tracker.py", line 111, in _update_info
    scanner = PortScanner()
  File "/usr/local/lib/python3.6/site-packages/nmap/nmap.py", line 155, in __init__
    raise PortScannerError('nmap program was not found in path')
nmap.nmap.PortScannerError: 'nmap program was not found in path'

i have home assistant on my home server installed using this method
https://github.com/home-assistant/hassio-build/tree/master/install#install-hassio

any idea?