don't overwrite list

problem:
assigning a list of animals to the list variable overwrites the list function, so that later in line 531 the list function is not available and raises a Type Error:
```
In [133]: list(filled_dict.keys())
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-133-a2c520b90051> in <module>
----> 1 list(filled_dict.keys())

TypeError: 'list' object is not callable
```
solution:
use another variable name instead of list

python3.html.markdown

@@ -466,8 +466,8 @@ prints:
     1 cat
     2 mouse
 """
-list = ["dog", "cat", "mouse"]
-for i, value in enumerate(list):
+animals = ["dog", "cat", "mouse"]
+for i, value in enumerate(animals):
     print(i, value)
 
 """