DOC: Simplify excel style example

Author: TomAugspurger

doc/source/whatsnew/v0.20.0.txt

@@ -393,6 +393,7 @@ For example, after running the following, ``styled.xlsx`` renders as below:
    df
    styled = df.style.\
        applymap(lambda val: 'color: %s' % 'red' if val < 0 else 'black').\
+       highlight_max()
        apply(lambda s: ['background-color: yellow' if v else ''
                         for v in s == s.max()])
    styled.to_excel('styled.xlsx', engine='openpyxl')