db.py adjust tag name size

It would seem some systems have a limit to the size a unique varchar can
be. This issue was preventing the use of the application due to the
databse rejecting the creation of the table.

server/web2py/applications/vidjil/models/db.py

@@ -257,7 +257,7 @@ db.define_table('user_log',
                 Field('record_id', 'integer'))
 
 db.define_table('tag',
-                Field('name', 'string', unique=True))
+                Field('name', 'string', length=255, unique=True))
 
 db.define_table('group_tag',
                 Field('group_id', 'reference auth_group'),