Update .nitignore

Author: LamentXU123

Doc/tools/.nitignore

@@ -16,7 +16,6 @@ Doc/library/ast.rst
 Doc/library/asyncio-extending.rst
 Doc/library/email.charset.rst
 Doc/library/email.parser.rst
-Doc/library/functools.rst
 Doc/library/http.cookiejar.rst
 Doc/library/http.server.rst
 Doc/library/importlib.rst