Clean out spinner character when done.

Details:
- The loop that writes the spinner characters already attempts to
  have a clean output when the spinner is sopped, by ending with
  the backslash character. However, there was no flush after the
  write of the backslash, so that the last spinner character
  could still be seen. This change adds a flush after the
  writing of the backslash.

Signed-off-by: Andreas Maier <[email protected]>

click_spinner/__init__.py

@@ -30,6 +30,7 @@ def init_spin(self):
             sys.stdout.flush()
             time.sleep(0.25)
             sys.stdout.write('\b')
+            sys.stdout.flush()
 
     def __enter__(self):
         self.start()