Messages sent by `Slack notifications` for Merge Requests are badly formatted

Summary

The messages sent by the "Slack notifications" integrations are wrong: Merge Requests events should contain a proper link to the MR.

Steps to reproduce

Gitlab version: 9.2.4-ee (c771fef)

I'm running a Gitlab-ee instance using Docker: 
docker run --detach \
    --hostname my.domain \
    --publish 8181:8181 \
    --publish 9022:22 \
    --add-host my.hook.domain:192.168.1.8 \
    --volume /srv/gitlab/config:/etc/gitlab \
    --volume /srv/gitlab/logs:/var/log/gitlab \
    --volume /srv/gitlab/data:/var/opt/gitlab \
    --restart always \
    --name gitlab \
    gitlab/gitlab-ee:latest

I have a project configured with Slack notifications enabled for Merge Requests (in Project > Settings > Integrations > Slack notifications), which send messages to a Slack channel called gitlab.

Doing any action on a Merge Request (open, approve, or merge) triggers the hook and sends a message to my Slack channel, but it looks like there's a typo in the message.

What is the current bug behavior?

Raw message received:

bob opened [!123 My merge request title](http://my.gitlab.domain/my/project/merge_requests/123) in my/project: My merge request title

What is the expected correct behavior?

Raw message I should receive (this was the case in a previous Gitlab version):

bob opened merge request !123 in my/project: My merge request title

Where merge request !123 is a link to http://my.gitlab.domain/my/project/merge_requests/123

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:		
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.3.3p222
Gem Version:	2.6.6
Bundler Version:1.13.7
Rake Version:	10.5.0
Redis Version:	3.2.5
Git Version:	2.11.1
Sidekiq Version:5.0.0

GitLab information
Version:	9.2.4-ee
Revision:	c771fef
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
DB Version:	9.6.1
URL:		http://my.domain
HTTP Clone URL:	http://my.domain/some-group/some-project.git
SSH Clone URL:	git@my.domain:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	yes
Using Omniauth:	no


GitLab Shell
Version:	5.0.4
Repository storage paths:
  • default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check 
Checking GitLab Shell ...

GitLab Shell version >= 5.0.4 ? ... OK (5.0.4)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
6/9 ... ok
6/11 ... ok
20/12 ... ok
12/13 ... ok
18/15 ... ok
6/16 ... ok
20/17 ... ok
20/19 ... ok
20/20 ... ok
20/21 ... ok
20/22 ... ok
5/23 ... ok
5/24 ... ok
5/25 ... ok
17/26 ... ok
18/27 ... ok
20/28 ... ok
5/29 ... ok
17/30 ... ok
26/31 ... ok
26/32 ... ok
26/33 ... ok
28/34 ... ok
17/35 ... ok
28/36 ... ok
17/37 ... repository is empty
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
Send ping to redis server: OK
gitlab-shell self-check successful


Checking GitLab Shell ... Finished


Checking Sidekiq ...


Running? ... yes
Number of Sidekiq processes ... 1


Checking Sidekiq ... Finished


Checking Reply by email ...


Reply by email is disabled in config/gitlab.yml


Checking Reply by email ... Finished


Checking LDAP ...


Server: ldapmain
LDAP authentication... Success
LDAP users with access to your GitLab server (only showing the first 100 results)
[...]


Checking LDAP ... Finished


Checking GitLab ...


Git configured with autocrlf=input? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config outdated? ... no
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory setup correctly? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
projects have namespace: ...
6/9 ... yes
6/11 ... yes
20/12 ... yes
12/13 ... yes
18/15 ... yes
6/16 ... yes
20/17 ... yes
20/19 ... yes
20/20 ... yes
20/21 ... yes
20/22 ... yes
5/23 ... yes
5/24 ... yes
5/25 ... yes
17/26 ... yes
18/27 ... yes
20/28 ... yes
5/29 ... yes
17/30 ... yes
26/31 ... yes
26/32 ... yes
26/33 ... yes
28/34 ... yes
17/35 ... yes
28/36 ... yes
17/37 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.1.0 ? ... yes (2.3.3)
Your git bin path is "/opt/gitlab/embedded/bin/git"
Git version >= 2.7.3 ? ... yes (2.11.1)
Active users: 22


Checking GitLab ... Finished

Possible fixes

Use the proper syntax for custom URLs in messages: https://api.slack.com/docs/message-formatting#linking_to_urls