Fix link to Style docs following nbsphinx move (pandas-dev#16062)

Author: jnothman

doc/source/whatsnew/v0.17.1.txt

@@ -58,7 +58,7 @@ We can render the HTML to get the following table.
    :file: whatsnew_0171_html_table.html
 
 :class:`~pandas.core.style.Styler` interacts nicely with the Jupyter Notebook.
-See the :ref:`documentation <style>` for more.
+See the :ref:`documentation <style.ipynb>` for more.
 
 .. _whatsnew_0171.enhancements:
 

doc/source/whatsnew/v0.20.0.txt

@@ -430,7 +430,7 @@ For example, after running the following, ``styled.xlsx`` renders as below:
     import os
     os.remove('styled.xlsx')
 
-See the :ref:`Style documentation <style>` for more detail.
+See the :ref:`Style documentation <style.ipynb>` for more detail.
 
 .. _whatsnew_0200.enhancements.intervalindex: