Picture 2.0 update fatal error: Class 'PictureMapping' not found

When upgrading to Picture 2.0 via Drush, the update fails with the following error:
PHP Fatal error: Class 'PictureMapping' not found in /path/to/sites/all/modules/contrib/picture/picture.install on line 105

In order to work around this error, I needed to download the new module without running the update, then rebuild the registry (drush rr), and then run drush updb.