Fix directory path for segment reader. (#169)
Fix directory path for segment reader. (#169)

Directory need to be changed because we updated dependency in https://github.com/Stackdriver/stackdriver-prometheus-sidecar/pull/143, in which there is breaking change on tsdb.LastCheckpoint() API.
Stackdriver/stackdriver-prometheus-sidecar,Stackdriver/stackdriver-prometheus-sidecar,Stackdriver/stackdriver-prometheus-sidecar