register: fix syntax error on python3.6

slapos/cli/register.py

@@ -279,7 +279,7 @@ def slapconfig(conf):
         to_replace.append(('ipv6_interface', conf.ipv6_interface))
 
     for key, value in to_replace:
-        cfg = re.sub('\n\s*%s\s*=.*' % key, '\n%s = %s' % (key, value), cfg)
+        cfg = re.sub('\n\\s*%s\\s*=.*' % key, '\n%s = %s' % (key, value), cfg)
 
     if not dry_run:
         with open(config_path, 'w') as fout: