default config file doesn't work

[stuxboulot]

Hi,

When i test this component, i have this error :
./grafana-annotation -verbose -data testjio -what "blabla" -tag test
grafana-annotation 2019/04/08 11:07:32 [CRIT] ▶ Unable to open configuration file.Get err #open ~/.grafana-anotation-poster.yml: no such file or directory

But this command work :
./grafana-annotation -config-file ~/.grafana-anotation-poster.yml -verbose -data testjio -what "blabla" -tag test
grafana-annotation 2019/04/08 11:07:55 [DEBU] ▶ new annotation with blabla 1554714475 [test] testjio
grafana-annotation 2019/04/08 11:07:55 [DEBU] ▶ {"what":"blabla","tags":["test"],"when":1554714475,"data":"testjio"}
grafana-annotation 2019/04/08 11:07:55 [DEBU] ▶ http://itc-mut-doc01.mut.parimutuel.local:31471/api/annotations/graphite
grafana-annotation 2019/04/08 11:07:56 [INFO] ▶ response Status:200 OK
grafana-annotation 2019/04/08 11:07:56 [INFO] ▶ response Headers:map[Content-Type:[application/json] Date:[Mon, 08 Apr 2019 09:09:39 GMT] Content-Length:[39]]
grafana-annotation 2019/04/08 11:07:56 [CRIT] ▶ error sending annotation. Message is Graphite annotation added

The default config file doesn't work.

[vfoucault]

Good on, Your PR seems good for this one.