Add an Prorate() function to reverse the noProrate() function

[yougotnet]

• Cashier Version: 9.3.0
• Laravel Version: 5.8+
• PHP Version: 7+
• Database Driver & Version:

Description:

The problem with the noProrate option is that when you execute a swap right afterward a swap with noProrate() function you can't turn on Prorate.

If I have a user downgrade the plan, I do not want to prorate or give a refund, but if the user downgrades and then upgrades higher to what the originally paid during the subscription period, then I want to swap to the original plan with noProrate and then swap to a higher plan with a Prorate.

What I did to fix the issue on my end is add a new function to the Subscription model called Prorate() so that I can turn the $prorate flag to true. If you would simply add the function to the base code it would help a lot of developers out.

Steps To Reproduce:

[driesvints]

Okay, I could see the benefit of this. Feel free to suggest something but please add a test as well.