fixed specs for list_from_json_array/1 and list_to_json_array/1

While I was getting rid of dialyzer warnings in my code, I found out that specs from list_to/from_json_array are more strict then success typing.

Initially I thought to introduce new 
```
-type json_term :: orddict() | binary() | integer() | float() | boolean() | 'undefined'.
```
and use it for both conversion functions, but in fact `list_to_json_array/1` accepts wider range of values than `list_from_json_array/1`, so I spec'ed them separately.