Use curly braces to specify an array value in helm set.
The latest versions of the chart need to have the additional arguments specified as a list or they error out:
```
Error: template: traefik/templates/_podtemplate.tpl:199:20: executing "traefik.podTemplate" at <.>: range can't iterate over --metrics.prometheus=true
```
Signed-off-by: Carson Anderson <carson.anderson@getweave.com>