textfile: fix duplicate metrics error (#738)
textfile: fix duplicate metrics error (#738)

The textfile gatherer should only be added to gatherer list once.

Signed-off-by: Li Wei <968ba988c540cee7ac38244330fb79805074b805@anbutu.com>
prometheus/node_exporter,prometheus/node_exporter,derekmarcotte/node_exporter,derekmarcotte/node_exporter,siavashs/node_exporter,derekmarcotte/node_exporter,siavashs/node_exporter,siavashs/node_exporter,prometheus/node_exporter,siavashs/node_exporter,derekmarcotte/node_exporter