[Observium] CE 0.16.1.7533 graph errors

Hi,

Firstly, a big thanks to the Dev team for releasing the latest CE version; very much appreciated.

Since the upgrade my "Custom traffic graphs" just have the "Error drawing graph" message.

Secondly, I also note the SNMP Statistic graphs on all devices have the same message.

As I just use Observium on my home network "because I can" none of this is critical for me but I'd thought I'd pass on my observations.

Thanks again for the release (my DD-WRT devices now report correctly ;-)).