Bump github.com/prometheus/client_golang from 1.14.0 to 1.15.0

Bumps [github.com/prometheus/client_golang](https://github.com/prometheus/client_golang) from 1.14.0 to 1.15.0.
- [Release notes](https://github.com/prometheus/client_golang/releases)
- [Changelog](https://github.com/prometheus/client_golang/blob/main/CHANGELOG.md)
- [Commits](prometheus/client_golang@v1.14.0...v1.15.0)

---
updated-dependencies:
- dependency-name: github.com/prometheus/client_golang
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

go.mod

@@ -5,7 +5,7 @@ go 1.15
 require (
 	github.com/bwmarrin/discordgo v0.27.1
 	github.com/joho/godotenv v1.5.1
-	github.com/prometheus/client_golang v1.14.0
+	github.com/prometheus/client_golang v1.15.0
 	github.com/stieneee/gopus v0.0.0-20210424193312-6d10f6090335
 	github.com/stieneee/gumble v0.0.0-20210424210604-732f48b5e0de
 	github.com/stieneee/tickerct v0.0.0-20210420020607-d1b092aa40e9