DOC: Fix delim_whitespace regex typo.

Minor typo in the explanation of delim_whitespace which tripped up a
user on SO (although the user should probably have been using
`delim_whitespace=True` directly anyhow.)

Author: dsm054 <dsm054@gmail.com>

Closes #13165 from dsm054/fix-delim_whitespace-regex and squashes the following commits:

c8f13d2 [dsm054] DOC: Fix delim_whitespace regex typo.

Author: dsm054

doc/source/io.rst

@@ -99,7 +99,7 @@ delimiter : str, default ``None``
   Alternative argument name for sep.
 delim_whitespace : boolean, default False
   Specifies whether or not whitespace (e.g. ``' '`` or ``'\t'``)
-  will be used as the delimiter. Equivalent to setting ``sep='\+s'``.
+  will be used as the delimiter. Equivalent to setting ``sep='\s+'``.
   If this option is set to True, nothing should be passed in for the
   ``delimiter`` parameter.
 

pandas/io/parsers.py

@@ -55,7 +55,7 @@
     Alternative argument name for sep.
 delim_whitespace : boolean, default False
     Specifies whether or not whitespace (e.g. ``' '`` or ``'\t'``) will be
-    used as the sep. Equivalent to setting ``sep='\+s'``. If this option
+    used as the sep. Equivalent to setting ``sep='\s+'``. If this option
     is set to True, nothing should be passed in for the ``delimiter``
     parameter.