[Doc] Capital latter in table column names are making confusion

In your [quick starting reference for python api](https://facebook.github.io/prophet/docs/quick_start.html#python-api) has a several tables that has capital letters in table column that is leading mis-understanding while it should be not capital in the dataframe:


When I checked the[ source code](https://github.com/facebook/prophet/blob/main/docs/_docs/quick_start.md), it seems it is non-capital. I guess some doc generation tool is making changes when compiling the md file to html.