Fix an edge case.

When sponges is use in foreground, and supervisor receive a kill signal,
it properly exits. But, the runner responsible of keeping sponges in
foreground will end up trying kill the supervisor on a "Ctrl-C". But,
the supervisor is already gone, and so ruby raise an "Errno::ESRCH"
exception.

Signed-off-by: chatgris <jboyer@af83.com>

lib/sponges/runner.rb

@@ -38,6 +38,8 @@ def trap_signals
 
     def kill_supervisor
       Process.kill :QUIT, @supervisor
+    rescue Errno::ESRCH => e
+      # Don't panic
     end
 
     def default_options