exit with 2 instead of 1 in case of ENOSPC

Signed-off-by: Mattia Rizzolo <mattia@debian.org>

diffoscope/main.py

@@ -734,7 +734,7 @@ def main(args=None):
         if e.errno != errno.ENOSPC:
             raise
         logger.error('No space left on device. Diffoscope exiting.')
-        sys.exit(1)
+        sys.exit(2)
     except KeyboardInterrupt:
         logger.error('Keyboard Interrupt')
         sys.exit(2)