Fix mutation observer check to not produce errors

src/definitions/modules/accordion.js

@@ -92,7 +92,7 @@ $.fn.accordion = function(parameters) {
         },
 
         observeChanges: function() {
-          if(MutationObserver !== undefined) {
+          if('MutationObserver' in window) {
             observer = new MutationObserver(function(mutations) {
               module.debug('DOM tree modified, updating selector cache');
               module.refresh();

src/definitions/modules/checkbox.js

@@ -105,7 +105,7 @@ $.fn.checkbox = function(parameters) {
         },
 
         observeChanges: function() {
-          if(MutationObserver !== undefined) {
+          if('MutationObserver' in window) {
             observer = new MutationObserver(function(mutations) {
               module.debug('DOM tree modified, updating selector cache');
               module.refresh();

src/definitions/modules/dropdown.js

@@ -102,7 +102,7 @@ $.fn.dropdown = function(parameters) {
         },
 
         observeChanges: function() {
-          if(MutationObserver !== undefined) {
+          if('MutationObserver' in window) {
             observer = new MutationObserver(function(mutations) {
               module.debug('DOM tree modified, updating selector cache');
               module.refresh();

src/definitions/modules/sticky.js

@@ -122,7 +122,7 @@ $.fn.sticky = function(parameters) {
           var
             context = $context[0]
           ;
-          if(MutationObserver !== undefined) {
+          if('MutationObserver' in window) {
             observer = new MutationObserver(function(mutations) {
               clearTimeout(module.timer);
               module.timer = setTimeout(function() {