Fix typo

Author: robsdedude

Doc/library/signal.rst

@@ -71,7 +71,7 @@ Besides, only the main thread of the main interpreter is allowed to set a new si
 .. warning::
 
    Synchronization primitives such as :class:`threading.Lock` must not be shared
-   between between signal handlers and other threads.
+   between signal handlers and other threads.
    Because blocking synchronization calls can be interrupted by signals,
    such sharing can lead to surprising dead locks.