build(deps): bump github.com/itzg/go-flagsfiller from 1.4.2 to 1.8.0 (#40)

Bumps [github.com/itzg/go-flagsfiller](https://github.com/itzg/go-flagsfiller) from 1.4.2 to 1.8.0.
- [Release notes](https://github.com/itzg/go-flagsfiller/releases)
- [Commits](https://github.com/itzg/go-flagsfiller/compare/v1.4.2...v1.8.0)

---
updated-dependencies:
- dependency-name: github.com/itzg/go-flagsfiller
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/go-kit/kit v0.9.0
 	github.com/gorilla/mux v1.8.0
 	github.com/influxdata/influxdb1-client v0.0.0-20191209144304-8bf82d3c094d
-	github.com/itzg/go-flagsfiller v1.4.2
+	github.com/itzg/go-flagsfiller v1.8.0
 	github.com/juju/ratelimit v1.0.1
 	github.com/pires/go-proxyproto v0.6.1
 	github.com/pkg/errors v0.9.1