Bump github.com/slack-go/slack from 0.7.4 to 0.8.0 (#20)

Bumps [github.com/slack-go/slack](https://github.com/slack-go/slack) from 0.7.4 to 0.8.0.
- [Release notes](https://github.com/slack-go/slack/releases)
- [Changelog](https://github.com/slack-go/slack/blob/master/CHANGELOG.md)
- [Commits](slack-go/slack@v0.7.4...v0.8.0)

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

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

go.mod

@@ -14,7 +14,7 @@ require (
 	github.com/mitchellh/go-wordwrap v1.0.1 // indirect
 	github.com/mitchellh/mapstructure v1.3.3 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
-	github.com/slack-go/slack v0.7.4
+	github.com/slack-go/slack v0.8.0
 	github.com/stretchr/testify v1.7.0
 	github.com/zclconf/go-cty v1.7.0 // indirect
 	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 // indirect

go.sum

@@ -299,8 +299,8 @@ github.com/sergi/go-diff v1.0.0 h1:Kpca3qRNrduNnOQeazBd0ysaKrUJiIuISHxogkT9RPQ=
 github.com/sergi/go-diff v1.0.0/go.mod h1:0CfEIISq7TuYL3j771MWULgwwjU+GofnZX9QAmXWZgo=
 github.com/sergi/go-diff v1.1.0 h1:we8PVUC3FE2uYfodKH/nBHMSetSfHDR6scGdBi+erh0=
 github.com/sergi/go-diff v1.1.0/go.mod h1:STckp+ISIX8hZLjrqAeVduY0gWCT9IjLuqbuNXdaHfM=
-github.com/slack-go/slack v0.7.4 h1:Z+7CmUDV+ym4lYLA4NNLFIpr3+nDgViHrx8xsuXgrYs=
-github.com/slack-go/slack v0.7.4/go.mod h1:FGqNzJBmxIsZURAxh2a8D21AnOVvvXZvGligs4npPUM=
+github.com/slack-go/slack v0.8.0 h1:ANyLY5KHLV+MxLJDQum2IuHTLwbCbDtaWY405X1EU9U=
+github.com/slack-go/slack v0.8.0/go.mod h1:FGqNzJBmxIsZURAxh2a8D21AnOVvvXZvGligs4npPUM=
 github.com/spf13/pflag v1.0.2/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 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=