fix a typo in Base.split (#18008)

* fix a typo in Base.split

* fixup! fix a typo in Base.split

base/docs/helpdb/Base.jl

@@ -1226,7 +1226,7 @@ Return an array of substrings by splitting the given string on occurrences of th
 character delimiters, which may be specified in any of the formats allowed by `search`'s
 second argument (i.e. a single character, collection of characters, string, or regular
 expression). If `chars` is omitted, it defaults to the set of all space characters, and
-`keep` is taken to be `false`. The two keyword arguments are optional: they are are a
+`keep` is taken to be `false`. The two keyword arguments are optional: they are a
 maximum size for the result and a flag determining whether empty fields should be kept in
 the result.
 """

doc/stdlib/strings.rst

@@ -259,7 +259,7 @@
 
  .. Docstring generated from Julia source
 
- Return an array of substrings by splitting the given string on occurrences of the given character delimiters, which may be specified in any of the formats allowed by ``search``\ 's second argument (i.e. a single character, collection of characters, string, or regular expression). If ``chars`` is omitted, it defaults to the set of all space characters, and ``keep`` is taken to be ``false``\ . The two keyword arguments are optional: they are are a maximum size for the result and a flag determining whether empty fields should be kept in the result.
+ Return an array of substrings by splitting the given string on occurrences of the given character delimiters, which may be specified in any of the formats allowed by ``search``\ 's second argument (i.e. a single character, collection of characters, string, or regular expression). If ``chars`` is omitted, it defaults to the set of all space characters, and ``keep`` is taken to be ``false``\ . The two keyword arguments are optional: they are a maximum size for the result and a flag determining whether empty fields should be kept in the result.
 
 .. function:: rsplit(string, [chars]; limit=0, keep=true)