lib/core: Fix ‘Since’ line for ostree_validate_remote_name()
lib/core: Fix ‘Since’ line for ostree_validate_remote_name()

This was missed when cherry-picking it out of
https://github.com/ostreedev/ostree/pull/924#discussion_r123097919.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #950
Approved by: cgwalters

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree