build(deps): bump github.com/slack-go/slack from 0.9.0 to 0.9.1

Bumps [github.com/slack-go/slack](https://github.com/slack-go/slack) from 0.9.0 to 0.9.1.
- [Release notes](https://github.com/slack-go/slack/releases)
- [Changelog](https://github.com/slack-go/slack/blob/master/CHANGELOG.md)
- [Commits](slack-go/slack@v0.9.0...v0.9.1)

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

go.mod

@@ -22,7 +22,7 @@ require (
 	github.com/rollbar/rollbar-go v1.4.0
 	github.com/shirou/gopsutil/v3 v3.21.4
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
-	github.com/slack-go/slack v0.9.0
+	github.com/slack-go/slack v0.9.1
 	github.com/sourcegraph/checkup v1.0.1-0.20200721114922-77e7567835d4
 	github.com/spaolacci/murmur3 v1.1.0
 	github.com/spf13/pflag v1.0.5 // indirect