[Simple Linked List]: Updated Stub File (#3834)

* Reworked stub to clean up mutable default argument and missing special method.

* Added bethanyg as contributor.

Author: BethanyG

exercises/practice/simple-linked-list/.meta/config.json

@@ -3,6 +3,7 @@
     "cmccandless"
   ],
   "contributors": [
+    "Bethanyg",
     "Dog",
     "N-Parsons",
     "rootulp",

exercises/practice/simple-linked-list/simple_linked_list.py

@@ -1,3 +1,7 @@
+class EmptyListException(Exception):
+    pass
+
+
 class Node:
     def __init__(self, value):
         pass
@@ -10,7 +14,10 @@ def next(self):
 
 
 class LinkedList:
-    def __init__(self, values=[]):
+    def __init__(self, values=None):
+        pass
+
+    def __iter__(self):
         pass
 
     def __len__(self):
@@ -27,7 +34,3 @@ def pop(self):
 
     def reversed(self):
         pass
-
-
-class EmptyListException(Exception):
-    pass