Updated NumFOCUS donation link

[lisamartin72]

Hi, I am a new staff member at NumFOCUS. We have updated our donation provider from Flipcause to Salsa. The new link is:

https://numfocus.salsalabs.org/donate-to-stan/index.html

Please update your website accordingly. : )

Thanks,

Lisa Martin
NumFOCUS

[bob-carpenter]

Thanks for posting the link. I'm going to use the issue mover to move it to our web site repo.

[bob-carpenter]

App mover is down. I'll do it by hand. Relocated issue on the web site rep os at:

stan-dev/stan-dev.github.io#81