Return different return code on KeyboardInterrupt

As I haven't found any good source for choice of exit code, I took value
130 found here:

http://tldp.org/LDP/abs/html/exitcodes.html

osc/babysitter.py

@@ -78,7 +78,7 @@ def run(prg, argv=None):
         return 1
     except KeyboardInterrupt:
         print('interrupted!', file=sys.stderr)
-        return 1
+        return 130
     except oscerr.UserAbort:
         print('aborted.', file=sys.stderr)
         return 1