FIX: ember 3 support (#23)

assets/javascripts/discourse-assign/connectors/topic-footer-main-buttons-before-create/assign-button.hbs

@@ -1,13 +1,13 @@
 {{#if topic.assigned_to_user.username}}
 {{d-button class="btn-default assign"
            icon="user-times"
-           action="unassign"
+           action=(action "unassign")
            label="discourse_assign.unassign.title"
            title="discourse_assign.unassign.help"}}
 {{else}}
 {{d-button class="btn-default assign"
            icon="user-plus"
-           action="assign"
+           action=(action "assign")
            label="discourse_assign.assign.title"
            title="discourse_assign.assign.help"}}
 {{/if}}

assets/javascripts/discourse/templates/modal/assign-user.hbs

@@ -20,5 +20,5 @@
 {{/d-modal-body}}
 
 <div class="modal-footer">
-{{d-button label='discourse_assign.assign_modal.assign' icon=inviteIcon action="assign" class="btn-primary" disabled=disabled}}
+{{d-button label='discourse_assign.assign_modal.assign' icon=inviteIcon action=(action "assign") class="btn-primary" disabled=disabled}}
 </div>