fix(elasticsearch): minor markup fix

public/app/plugins/datasource/elasticsearch/partials/metricAgg.html

@@ -2,7 +2,8 @@
 	<ul class="tight-form-list">
 		<li class="tight-form-item query-keyword tight-form-align" style="width: 75px;">
 			Metric
-			&nbsp; <a ng-click="toggleShowMetric()" bs-tooltip="Click to toggle show/hide metric">
+			&nbsp;
+			<a ng-click="toggleShowMetric()" bs-tooltip="'Click to toggle show / hide metric'">
 				<i class="fa fa-eye" ng-hide="agg.hide"></i>
 				<i class="fa fa-eye-slash" ng-show="agg.hide"></i>
 			</a>