Updated typo in entrywidthmode for legend

The current version of the doc shows that the `entrywidthmode` can either be `pixels` (by default) or set to `fraction`. But fraction was written as `'fraction` without the trailing single quote. This merge request fixes that typo.

Author: tanmaychimurkar

doc/python/legend.md

@@ -193,7 +193,7 @@ fig.show()
 
 *New in 5.11*
 
-Set the width of horizontal legend entries by setting `entrywidth`. Here we set it to `70` pixels. Pixels is the default unit for `entrywidth`, but you can set it to be a fraction of the plot width using `entrywidthmode='fraction`.
+Set the width of horizontal legend entries by setting `entrywidth`. Here we set it to `70` pixels. Pixels is the default unit for `entrywidth`, but you can set it to be a fraction of the plot width using `entrywidthmode='fraction'`.
 
 ```python
 import plotly.express as px