Update .nitignore

Author: LamentXU123

Doc/tools/.nitignore

@@ -38,7 +38,6 @@ Doc/library/tkinter.rst
 Doc/library/tkinter.scrolledtext.rst
 Doc/library/tkinter.ttk.rst
 Doc/library/unittest.mock.rst
-Doc/library/unittest.rst
 Doc/library/urllib.parse.rst
 Doc/library/urllib.request.rst
 Doc/library/wsgiref.rst