[semver:patch] fixes install_promtool command

[dgeorges]

SEMVER Update Type:

• Major
• Minor
• Patch

Description:

fixes error during promtool install.
see prometheus/prometheus#8480

Motivation:

fixes:

#!/bin/bash -eo pipefail
go get github.com/prometheus/prometheus/cmd/promtool
# github.com/prometheus/prometheus/cmd/promtool
/go/src/github.com/prometheus/prometheus/cmd/promtool/main.go:642:35: not enough arguments in call to api.LabelValues
	have (context.Context, string, time.Time, time.Time)
	want (context.Context, string, []string, time.Time, time.Time)

Exited with code exit status 2