Use hashrocket for dasherized attribute

Signed-off-by: Rémy Coutable <remy@rymai.me>

app/views/projects/merge_requests/widget/open/_approvals_footer.html.haml

-%approvals-footer{ 'pending-avatar-svg' => custom_icon('icon_dotted_circle'), 'checkmark-svg' => custom_icon('icon_checkmark'), ':user-can-approve' => 'approvals.user_can_approve', ':user-has-approved' => 'approvals.user_has_approved', ':approved-by' => 'approvals.approved_by', ':approvals-left':'approvals.approvals_left' }
+%approvals-footer{ 'pending-avatar-svg' => custom_icon('icon_dotted_circle'), 'checkmark-svg' => custom_icon('icon_checkmark'), ':user-can-approve' => 'approvals.user_can_approve', ':user-has-approved' => 'approvals.user_has_approved', ':approved-by' => 'approvals.approved_by', ':approvals-left' => 'approvals.approvals_left' }