Channel link marker changed from ! to ~ (#4433)

Fixes PLT-4570

api/slackimport.go

@@ -440,7 +440,7 @@ func SlackConvertChannelMentions(channels []SlackChannel, posts map[string][]Sla
 			l4g.Warn(utils.T("api.slackimport.slack_convert_channel_mentions.compile_regexp_failed.warn"), channel.Id, channel.Name)
 			continue
 		}
-		regexes["!"+channel.Name] = r
+		regexes["~"+channel.Name] = r
 	}
 
 	for channelName, channelPosts := range posts {

api/slackimport_test.go

@@ -110,10 +110,10 @@ func TestSlackConvertChannelMentions(t *testing.T) {
 	expectedPosts := map[string][]SlackPost{
 		"test-channel": {
 			{
-				Text: "Go to !one.",
+				Text: "Go to ~one.",
 			},
 			{
-				Text: "Try !two for this.",
+				Text: "Try ~two for this.",
 			},
 		},
 	}