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, 5 insertions, 5 deletions

diff --git a/spec/services/system_note_service_spec.rb b/spec/services/system_note_service_spec.rb
index 00427d6db2a..3d854a959f3 100644
--- a/spec/services/system_note_service_spec.rb
+++ b/spec/services/system_note_service_spec.rb
@@ -330,13 +330,13 @@ describe SystemNoteService, services: true do
             let(:mentioner) { project2.repository.commit }
 
             it 'references the mentioning commit' do
-              expect(subject.note).to eq "mentioned in commit #{mentioner.to_reference(project)}"
+              expect(subject.note).to eq "Mentioned in commit #{mentioner.to_reference(project)}"
             end
           end
 
           context 'from non-Commit' do
             it 'references the mentioning object' do
-              expect(subject.note).to eq "mentioned in issue #{mentioner.to_reference(project)}"
+              expect(subject.note).to eq "Mentioned in issue #{mentioner.to_reference(project)}"
             end
           end
         end
@@ -346,13 +346,13 @@ describe SystemNoteService, services: true do
             let(:mentioner) { project.repository.commit }
 
             it 'references the mentioning commit' do
-              expect(subject.note).to eq "mentioned in commit #{mentioner.to_reference}"
+              expect(subject.note).to eq "Mentioned in commit #{mentioner.to_reference}"
             end
           end
 
           context 'from non-Commit' do
             it 'references the mentioning object' do
-              expect(subject.note).to eq "mentioned in issue #{mentioner.to_reference}"
+              expect(subject.note).to eq "Mentioned in issue #{mentioner.to_reference}"
             end
           end
         end
@@ -362,7 +362,7 @@ describe SystemNoteService, services: true do
 
   describe '.cross_reference?' do
     it 'is truthy when text begins with expected text' do
-      expect(described_class.cross_reference?('mentioned in something')).to be_truthy
+      expect(described_class.cross_reference?('Mentioned in something')).to be_truthy
     end
 
     it 'is falsey when text does not begin with expected text' do