fix(collection): correctly shallow clone passed in options

Author: mbroadst

lib/db.js

@@ -313,7 +313,7 @@ const collectionKeys = [
 Db.prototype.collection = function(name, options, callback) {
   if (typeof options === 'function') (callback = options), (options = {});
   options = options || {};
-  Object.assign({}, options);
+  options = Object.assign({}, options);
 
   // Set the promise library
   options.promiseLibrary = this.s.promiseLibrary;