Fix typo in mock docs.
diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst
index 3e50031..8e72696 100644
--- a/Doc/library/unittest.mock.rst
+++ b/Doc/library/unittest.mock.rst
@@ -1,3 +1,4 @@
+
:mod:`unittest.mock` --- mock object library
============================================
@@ -646,7 +647,7 @@
which have no meaning on a non-callable mock.
Mock objects that use a class or an instance as a `spec` or `spec_set` are able
-to pass `isintance` tests:
+to pass `isinstance` tests:
>>> mock = Mock(spec=SomeClass)
>>> isinstance(mock, SomeClass)