Merge branch 'capitalize-mentioned-issue-notes' into 'master'

Capitalize mentioned issue timeline notes

## What does this MR do?
Renames `mentioned in` to `Mentioned in` for issue timeline notes

## Are there points in the code the reviewer needs to double check?
Shouldn't be any :smile: 

## Why was this MR needed?
Resolves existing UI inconsistency as all the other issue timeline notes have their first letter capitalized.

## What are the relevant issue numbers?
Closes #21416 

## Screenshots (if relevant)
Before:
![Screen_Shot_2016-08-25_at_10.52.47_AM](/uploads/61de0a7d65fd739a6e565f6e63d2f52d/Screen_Shot_2016-08-25_at_10.52.47_AM.png)

After:
![Screen_Shot_2016-08-25_at_10.52.05_AM](/uploads/f67f353c285453306d6b80578b11e587/Screen_Shot_2016-08-25_at_10.52.05_AM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6028

1 files changed, 1 insertions, 1 deletions

diff --git a/features/steps/shared/issuable.rb b/features/steps/shared/issuable.rb
index aa666a954bc..df9845ba569 100644
--- a/features/steps/shared/issuable.rb
+++ b/features/steps/shared/issuable.rb
@@ -179,7 +179,7 @@ module SharedIssuable
     project = Project.find_by(name: from_project_name)
 
     expect(page).to have_content(user_name)
-    expect(page).to have_content("mentioned in #{issuable.class.to_s.titleize.downcase} #{issuable.to_reference(project)}")
+    expect(page).to have_content("Mentioned in #{issuable.class.to_s.titleize.downcase} #{issuable.to_reference(project)}")
   end
 
   def expect_sidebar_content(content)