Merge branch 'cross-project-reference-typo-fix' into 'master'

changes verb `references` to noun `reference`.

See merge request !2349

app/views/shared/issuable/_sidebar.html.haml

@@ -74,7 +74,7 @@
       .title
       .cross-project-reference
         %span#cross-project-reference
-          References:
+          Reference:
           %a{href: '#', title:project_ref}
             = project_ref
         = clipboard_button(clipboard_target: 'span#cross-project-reference')