Merge branch 'heavy-weights' into 'master'

Set default_label attribute on weight issue filter.

The label for the "Weight" filter in the issues list is darker than the other filters. 

This MR sets the `default_label` attribute to 'Weight', so that the styles for default labels are applied to "Weight". This is the convention for other filter dropdowns. 

I'm guessing it regressed here 8961364c. The default_label was not set when the weight filter was originally transitioned to the new dropdown (https://gitlab.com/gitlab-org/gitlab-ee/commit/b0639b1fdafd0cf48f1fcdaa8047f7414010e643). I'm guessing some styles were unintentionally cascading to give this the correct look, and were changed.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/1094

See merge request !794

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

@@ -34,7 +34,7 @@
             - if params[:weight]
               = hidden_field_tag(:weight, params[:weight])
             = dropdown_tag("Weight", options: { title: "Filter by weight", toggle_class: 'js-weight-select js-filter-submit', dropdown_class: "dropdown-menu-selectable",
-              placeholder: "Search weight", data: { field_name: "weight" } }) do
+              placeholder: "Search weight", data: { field_name: "weight" , default_label: "Weight" } }) do
               %ul
                 - Issue.weight_options.each do |weight|
                   %li