signal handler should only be called with 2 args

I accidentally added "self" as first parameter to the signal handler
method. Of course it is not called with a class instance, the signal
handler always only receives 2 parameters: the signal number and the
stack frame. So just removing the self fixes things.

Proposed-by: Christian Holme <cholme@gmx.com>
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/init.py

@@ -249,7 +249,7 @@ class OfflineImap:
         self.lock(config, ui)
 
     
-        def sigterm_handler(self, signum, frame):
+        def sigterm_handler(signum, frame):
             # die immediately
             ui = getglobalui()
             ui.terminate(errormsg="terminating...")