Remove element from array once the src is set

I think this is what was intended.  Elements are removed from `store` once the src is set to the data-echo attribute.

src/echo.js

@@ -10,19 +10,18 @@ window.Echo = (function (window, document, undefined) {
   };
 
   var _pollImages = function () {
-    for (var i = 0; i < store.length; i++) {
+    for (var i = 0, len = store.length; i < len; i++) {
       var self = store[i];
       if (_inView(self)) {
         self.src = self.getAttribute('data-echo');
-        if ([].indexOf && [].slice.call(store).indexOf(self) !== -1) {
-          [].slice.call(store).splice(i, 1);
-        }
+        store.splice(i, 1);
       }
     }
   };
 
   var init = function () {
     store = document.querySelectorAll('[data-echo]');
+    store = [].slice.call(store);
     _pollImages();
     window.onscroll = _pollImages;
   };