Correct minor grammatical mistake in open docs (GH-15865)

(cherry picked from commit 05184515f924c3880067aad87940dd466f751585)

Co-authored-by: Andre Delfino <adelfino@gmail.com>
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index a4097b0..9ea7b7b 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -1072,8 +1072,8 @@
    ========= ===============================================================
 
    The default mode is ``'r'`` (open for reading text, synonym of ``'rt'``).
-   Modes ``'w+'`` and ``'w+b'`` opens and truncates the file.  Modes ``'r+'``
-   and ``'r+b'`` opens the file with no truncation.
+   Modes ``'w+'`` and ``'w+b'`` open and truncate the file.  Modes ``'r+'``
+   and ``'r+b'`` open the file with no truncation.
 
    As mentioned in the :ref:`io-overview`, Python distinguishes between binary
    and text I/O.  Files opened in binary mode (including ``'b'`` in the *mode*