[docs] [issue29772] Unintentionally deleted line on library/collections.rst

[Serhiy Storchaka]

Changes by Serhiy Storchaka <storchaka+cpython at gmail.com>:


----------
nosy: +serhiy.storchaka

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29772>
_______________________________________