Improve check for analytics function option

lib/proto/parse-options.js

@@ -9,7 +9,7 @@ module.exports = function(options) {
   this.options.switches = this.options.switches || {}
   this.options.switchesOptions = this.options.switchesOptions || {}
   this.options.history = this.options.history || true
-  this.options.analytics = this.options.analytics || function() {
+  this.options.analytics = (typeof this.options.analytics === "function") ? this.options.analytics : function() {
     if (window._gaq) {
       _gaq.push(["_trackPageview"])
     }