fix typo

Author: rouilj

roundup/configuration.py

@@ -830,7 +830,7 @@ def str2value(self, value):
 
 
 class SessiondbBackendOption(Option):
-    """Make sure that sessiondb is compatile with the primary db.
+    """Make sure that sessiondb is compatible with the primary db.
        Fail with error and suggestions if they are incompatible.
     """