Add space next to download icon in download artifacts button

app/views/projects/artifacts/browse.html.haml

@@ -18,7 +18,7 @@
     .tree-controls<
       = link_to download_project_job_artifacts_path(@project, @build),
         rel: 'nofollow', download: '', class: 'gl-button btn btn-default download' do
-        = sprite_icon('download')
+        = sprite_icon('download', css_class: 'gl-mr-2')
         Download artifacts archive
 
   .tree-content-holder