Placeholder on milestone form

Updated JS spec to include gl_form

app/views/projects/milestones/_form.html.haml

@@ -10,7 +10,7 @@
         = f.label :description, "Description", class: "control-label"
         .col-sm-10
           = render layout: 'projects/md_preview', locals: { preview_class: "md-preview" } do
-            = render 'projects/zen', f: f, attr: :description, classes: 'note-textarea'
+            = render 'projects/zen', f: f, attr: :description, classes: 'note-textarea', placeholder: 'Write milestone description...'
             = render 'projects/notes/hints'
           .clearfix
           .error-alert

spec/javascripts/notes_spec.js.coffee

 #= require notes
+#= require gl_form
 
 window.gon = {}
 window.disableButtonIfEmptyField = -> null