fix(alerting): replace one hack with another hack

public/app/features/alerting/partials/alert_tab.html

@@ -123,7 +123,7 @@
 			</div>
 		</div>
 
-		<div class="gf-form-group" style="width: 60%; margin-left: 8rem;" ng-if="ctrl.subTabIndex === 2">
+		<div class="gf-form-group" style="max-width: 720px;" ng-if="ctrl.subTabIndex === 2">
 			<h5 class="section-heading">Alert history</h5>
 			<section class="card-section card-list-layout-list">
 				<ol class="card-list" >