Restore [] where default arguments are not keywords
Reverts some changes of a36666c52115.
In the case of os's `mknod(filename[, mode=0600[, device=0]])`, I have nested
the [] as setting mode doesn't require to set device (but setting device
requires to set mode).
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 477ea86..a553d09 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -627,7 +627,7 @@
break
-.. function:: tee(iterable, n=2)
+.. function:: tee(iterable[, n=2])
Return *n* independent iterators from a single iterable. Equivalent to::