chore(deps): bump github.com/slack-go/slack from 0.15.0 to 0.16.0

Bumps [github.com/slack-go/slack](https://github.com/slack-go/slack) from 0.15.0 to 0.16.0.
- [Release notes](https://github.com/slack-go/slack/releases)
- [Changelog](https://github.com/slack-go/slack/blob/master/history.go)
- [Commits](slack-go/slack@v0.15.0...v0.16.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

go.mod

@@ -9,7 +9,7 @@ require (
 	github.com/kelseyhightower/envconfig v1.4.0
 	github.com/pkg/errors v0.9.1
 	github.com/sirupsen/logrus v1.9.3
-	github.com/slack-go/slack v0.15.0
+	github.com/slack-go/slack v0.16.0
 	golang.org/x/oauth2 v0.29.0
 	gopkg.in/errgo.v2 v2.1.0
 	gopkg.in/yaml.v3 v3.0.1

go.sum

@@ -69,8 +69,8 @@ github.com/rogpeppe/go-internal v1.13.1 h1:KvO1DLK/DRN07sQ1LQKScxyZJuNnedQ5/wKSR
 github.com/rogpeppe/go-internal v1.13.1/go.mod h1:uMEvuHeurkdAXX61udpOXGD/AzZDWNMNyH2VO9fmH0o=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
 github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
-github.com/slack-go/slack v0.15.0 h1:LE2lj2y9vqqiOf+qIIy0GvEoxgF1N5yLGZffmEZykt0=
-github.com/slack-go/slack v0.15.0/go.mod h1:hlGi5oXA+Gt+yWTPP0plCdRKmjsDxecdHxYQdlMQKOw=
+github.com/slack-go/slack v0.16.0 h1:khp/WCFv+Hb/B/AJaAwvcxKun0hM6grN0bUZ8xG60P8=
+github.com/slack-go/slack v0.16.0/go.mod h1:hlGi5oXA+Gt+yWTPP0plCdRKmjsDxecdHxYQdlMQKOw=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=