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

src/libostree/ostree-core.c

@@ -187,7 +187,7 @@ ostree_validate_rev (const char *rev,
  * @error: Error
  *
  * Returns: %TRUE if @remote_name is a valid remote name
- * Since: 2017.7
+ * Since: 2017.8
  */
 gboolean
 ostree_validate_remote_name (const char  *remote_name,