Change donation redirect URL

Updated the donation redirect URL to the new donations page.

Author: daschuer

content/_redirects

@@ -30,7 +30,7 @@ https://www.mixxx.org/* https://mixxx.org/:splat                301!
 /wiki                             https://github.com/mixxxdj/mixxx/wiki                        301!
 
 # Redirect to donation page
-/donate https://www.opencollective.com/mixxx 302!
+/donate https://mixxx.org/donations/ 302!
 
 # Error page
 /*                      /error/                                 404