Fix miscellaneous typos (#4275)

diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index 6fdfdc4..b6eb8cc 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -2374,7 +2374,7 @@
     any new attribute on the sealed mock. The sealing process is performed recursively.
 
     If a mock instance is assigned to an attribute instead of being dynamically created
-    it wont be considered in the sealing chain. This allows to prevent seal from fixing
+    it won't be considered in the sealing chain. This allows to prevent seal from fixing
     part of the mock object.
 
         >>> mock = Mock()