[ui] fix activity heatmap popover

frappe/desk/page/activity/activity.js

@@ -157,7 +157,9 @@ frappe.activity.Feed = Class.extend({
 
 frappe.activity.render_heatmap = function(page) {
 	var me = this;
-	$('<div class="heatmap"></div><hr style="margin-bottom: 0px;">').prependTo(page.main);
+	$('<div class="heatmap-container" style="text-align:center">\
+		<div class="heatmap" style="display:inline-block;"></div></div>\
+		<hr style="margin-bottom: 0px;">').prependTo(page.main);
 
 	frappe.call({
 		method: "frappe.desk.page.activity.activity.get_heatmap_data",