Update slack vendor to fix regression (#959)

go.mod

@@ -64,7 +64,7 @@ require (
 	gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 // indirect
 )
 
-replace github.com/nlopes/slack v0.6.0 => github.com/matterbridge/slack v0.1.1-0.20191207211853-5b5f1326cdab
+replace github.com/nlopes/slack v0.6.0 => github.com/matterbridge/slack v0.1.1-0.20191208194820-95190f11bfb6
 
 replace github.com/bwmarrin/discordgo v0.19.0 => github.com/matterbridge/discordgo v0.0.0-20191026232317-01823f4ebba4
 

go.sum

@@ -138,6 +138,8 @@ github.com/matterbridge/logrus-prefixed-formatter v0.0.0-20180806162718-01618749
 github.com/matterbridge/logrus-prefixed-formatter v0.0.0-20180806162718-01618749af61/go.mod h1:iXGEotOvwI1R1SjLxRc+BF5rUORTMtE0iMZBT2lxqAU=
 github.com/matterbridge/slack v0.1.1-0.20191207211853-5b5f1326cdab h1:4eNOoF+qvyXTwmlD5PwEwPHEpYAUTh2KpEjmEZOSVyE=
 github.com/matterbridge/slack v0.1.1-0.20191207211853-5b5f1326cdab/go.mod h1:2uCJim0Ct2z1Uj+XQq47KCLLC1b/9UTYaZOvDtbZfK4=
+github.com/matterbridge/slack v0.1.1-0.20191208194820-95190f11bfb6 h1:UvXXR9tHYqJUXZVEtiK2qkEWBXfFneicate5kOshVFk=
+github.com/matterbridge/slack v0.1.1-0.20191208194820-95190f11bfb6/go.mod h1:2uCJim0Ct2z1Uj+XQq47KCLLC1b/9UTYaZOvDtbZfK4=
 github.com/mattermost/mattermost-server v5.5.0+incompatible h1:0wcLGgYtd+YImtLDPf2AOfpBHxbU4suATx+6XKw1XbU=
 github.com/mattermost/mattermost-server v5.5.0+incompatible/go.mod h1:5L6MjAec+XXQwMIt791Ganu45GKsSiM+I0tLR9wUj8Y=
 github.com/mattn/go-colorable v0.1.1 h1:G1f5SKeVxmagw/IyvzvtZE4Gybcc4Tr1tf7I8z0XgOg=

vendor/github.com/nlopes/slack/attachments.go

@@ -61,7 +61,7 @@ type ConfirmationField struct {
 // Attachment contains all the information for an attachment
 type Attachment struct {
 	Color    string `json:"color,omitempty"`
-	Fallback string `json:"fallback,omitempty"`
+	Fallback string `json:"fallback"`
 
 	CallbackID string `json:"callback_id,omitempty"`
 	ID         int    `json:"id,omitempty"`

vendor/modules.txt

@@ -138,7 +138,7 @@ github.com/nicksnyder/go-i18n/i18n
 github.com/nicksnyder/go-i18n/i18n/bundle
 github.com/nicksnyder/go-i18n/i18n/language
 github.com/nicksnyder/go-i18n/i18n/translation
-# github.com/nlopes/slack v0.6.0 => github.com/matterbridge/slack v0.1.1-0.20191207211853-5b5f1326cdab
+# github.com/nlopes/slack v0.6.0 => github.com/matterbridge/slack v0.1.1-0.20191208194820-95190f11bfb6
 github.com/nlopes/slack
 github.com/nlopes/slack/internal/errorsx
 github.com/nlopes/slack/internal/timex