design: fix spelling in adapters.txt

Change-Id: Id68f5bf016e87ae8582f09e71b1abdd7f4bfea5c
Signed-off-by: Patrice LUCAS <patrice.lucas@cea.fr>
Reviewed-on: https://gerrit.ccc.ocre.cea.fr/gerrit/c/phobos/+/7291

Tested-by: Jenkins s8open_nr <s8open_nr@ccc.ocre.cea.fr>
Reviewed-by: Sebastien Gougeaud <sebastien.gougeaud@cea.fr>
Reviewed-by: Thomas Leibovici <thomas.leibovici@cea.fr>

doc/design/adapters.txt

@@ -39,7 +39,7 @@ entries are addressed, organized, and accessed in this backend.
   (e.g. as extended attributes, or a metadata_blob). This information is critical
   to rebuild phobos database in case of accidental loss.
 
-- Adapater should provide an object-base interface: put/get/del
+- Adapters should provide an object-based interface: put/get/del
 
 - If possible, it must provide a feature to manage media transactions,
   that could be performed after writing an extent or after writing a set of