Cursor.Observe() 'removed' event are not firing (#38)

* Cursor.Observe() 'removed' event are not firing

I found that the 'removed' event in Cursor.Observe() are not firing, I guess its because 
`Data.db[collection].findOne({$and:[{_id:newDocument._id}, cursor._selector]})` returns null for deleted documents, maybe you can find a better solution than mine, thank you.

* Update Collection.js

Co-authored-by: Nathaniel Dsouza <[email protected]>

Author: makn3tiza

src/Collection.js

@@ -13,7 +13,10 @@ export const runObservers = (type, collection, newDocument, oldDocument) => {
   if(observers[collection]) {
     observers[collection].forEach(({cursor, callbacks}) => {
       if(callbacks[type]) {
-        if(Data.db[collection].findOne({$and:[{_id:newDocument._id}, cursor._selector]})) {
+        if(type === 'removed') {
+          callbacks['removed'](newDocument);
+        }
+        else if(Data.db[collection].findOne({$and:[{_id:newDocument._id}, cursor._selector]})) {
           try {
             callbacks[type](newDocument, oldDocument);
           }