Updated net/syncthing to 0.14.6

This is a minor release recommended for all users.

Resolved issues since v0.14.5:

#3496: In sync percentages no longer go negative for large numbers of deleted files.
#3502: Files that were deleted and then ignored are no longer deleted on other devices that didn't ignore them.
#3525: Configuration is no longer moved away when perfoming an upgrade on a full disk.

(abs)