Update dragster to support IE11 drag&drop

vendor/assets/javascripts/dragster.js

@@ -1,19 +1,17 @@
 
 (function() {
   var Dragster,
-    __bind = function(fn, me){ return function(){ return fn.apply(me, arguments); }; };
+      __bind = function(fn, me){ return function(){ return fn.apply(me, arguments); }; };
 
   Dragster = (function() {
     function Dragster(el) {
       this.el = el;
       this.dragleave = __bind(this.dragleave, this);
       this.dragenter = __bind(this.dragenter, this);
-      if (this.supportsEventConstructors()) {
-        this.first = false;
-        this.second = false;
-        this.el.addEventListener("dragenter", this.dragenter, false);
-        this.el.addEventListener("dragleave", this.dragleave, false);
-      }
+      this.first = false;
+      this.second = false;
+      this.el.addEventListener("dragenter", this.dragenter, false);
+      this.el.addEventListener("dragleave", this.dragleave, false);
     }
 
     Dragster.prototype.dragenter = function(event) {
@@ -21,13 +19,12 @@
         return this.second = true;
       } else {
         this.first = true;
-        return this.el.dispatchEvent(new CustomEvent("dragster:enter", {
-          bubbles: true,
-          cancelable: true,
-          detail: {
-            dataTransfer: event.dataTransfer
-          }
-        }));
+        this.customEvent = document.createEvent("CustomEvent");
+        this.customEvent.initCustomEvent("dragster:enter", true, true, {
+          dataTransfer: event.dataTransfer,
+          sourceEvent: event
+        });
+        return this.el.dispatchEvent(this.customEvent);
       }
     };
 
@@ -38,13 +35,12 @@
         this.first = false;
       }
       if (!this.first && !this.second) {
-        return this.el.dispatchEvent(new CustomEvent("dragster:leave", {
-          bubbles: true,
-          cancelable: true,
-          detail: {
-            dataTransfer: event.dataTransfer
-          }
-        }));
+        this.customEvent = document.createEvent("CustomEvent");
+        this.customEvent.initCustomEvent("dragster:leave", true, true, {
+          dataTransfer: event.dataTransfer,
+          sourceEvent: event
+        });
+        return this.el.dispatchEvent(this.customEvent);
       }
     };
 
@@ -53,15 +49,6 @@
       return this.el.removeEventListener("dragleave", this.dragleave, false);
     };
 
-    Dragster.prototype.supportsEventConstructors = function() {
-      try {
-        new CustomEvent("z");
-      } catch (_error) {
-        return false;
-      }
-      return true;
-    };
-
     Dragster.prototype.reset = function() {
       this.first = false;
       return this.second = false;