Fix typo in MR CSV export

Fixes a reference to merge_requests in an
email template.

app/views/notify/_issuable_csv_export.html.haml

 %p{ style: 'font-size:18px; text-align:center;  line-height:30px;' }
   - project_link = link_to(@project.full_name, project_url(@project), style: "color:#3777b0; text-decoration:none; display:block;")
-  = _('Your CSV export of %{count} from project %{project_link} has been added to this email as an attachment.').html_safe % { count: pluralize(@written_count, type.to_s), project_link: project_link }
+  = _('Your CSV export of %{count} from project %{project_link} has been added to this email as an attachment.').html_safe % { count: pluralize(@written_count, type.to_s.titleize.downcase), project_link: project_link }
   - if @truncated
     %p
       = _('This attachment has been truncated to avoid exceeding the maximum allowed attachment size of 15MB. %{written_count} of %{count} issues have been included. Consider re-exporting with a narrower selection of issues.') % { written_count: @written_count, count: @count }

spec/mailers/emails/merge_requests_spec.rb

@@ -52,7 +52,8 @@ RSpec.describe Emails::MergeRequests do
 
     it { expect(subject.subject).to eq("#{project.name} | Exported merge requests") }
     it { expect(subject.to).to contain_exactly(user.notification_email_for(project.group)) }
-    it { expect(subject).to have_content('Your CSV export of 10 merge requests from project')}
+    it { expect(subject.html_part).to have_content("Your CSV export of 10 merge requests from project") }
+    it { expect(subject.text_part).to have_content("Your CSV export of 10 merge requests from project") }
 
     context 'when truncated' do
       let(:export_status) do