BUGS.txt now points to GitHub Issues instead of bugzilla.libsdl.org.

BUGS.txt

@@ -1,7 +1,7 @@
 
-Bugs are now managed in the SDL bug tracker, here:
+Bugs are now managed in the SDL issue tracker, here:
 
-    https://bugzilla.libsdl.org/
+    https://github.com/libsdl-org/SDL/issues
 
 You may report bugs there, and search to see if a given issue has already
  been reported, discussed, and maybe even fixed.