Fix a bug

Change-Id: I5649c9f04cf3c1789f08f3c56d3021c2ec65a93a

src/markerclusterer.js

diff --git a/src/markerclusterer.js b/src/markerclusterer.js
index fc69cf1..466c41d 100644
--- a/src/markerclusterer.js
+++ b/src/markerclusterer.js
@@ -1079,7 +1079,7 @@
   if (this.visible_) {
     var pos = this.getPosFromLatLng_(this.center_);
     this.div_.style.cssText = this.createCss(pos);
-    this.div_.text = this.sums_.text;
+    this.div_.textContent = this.sums_.text;
   }
 
   var panes = this.getPanes();
@@ -1178,7 +1178,7 @@
   this.text_ = sums.text;
   this.index_ = sums.index;
   if (this.div_) {
-    this.div_.text = sums.text;
+    this.div_.textContent = sums.text;
   }
 
   this.useStyle();