Fix wording of the dashboard tags popover text

public/app/features/dashboard/partials/settings.html

@@ -28,7 +28,7 @@
 			<div class="gf-form">
 				<label class="gf-form-label width-7">
           Tags
-          <info-popover mode="right-normal">Press enter to a add tag</info-popover>
+          <info-popover mode="right-normal">Press enter to add a tag</info-popover>
         </label>
 				<bootstrap-tagsinput ng-model="dashboard.tags" tagclass="label label-tag" placeholder="add tags">
 				</bootstrap-tagsinput>