CI: On Sauce, mark screenshot jobs failure if error

This is just a little enhancement to how screenshot jobs show up in the
Sauce Labs dashboard; if no status is set they'll be a question mark,
but if a screenshot job has an error (other than fetching browser logs),
it should be marked a failure (which'll be a nice red X in the Sauce
Labs dashboard).

script/screenshots.js

diff --git a/script/screenshots.js b/script/screenshots.js
index b230a7e..63d9374 100644
--- a/script/screenshots.js
+++ b/script/screenshots.js
@@ -192,6 +192,7 @@
   .fail(function(err) {
     console.log('ERROR:', browser.config.browserName, browser.config.platform);
     console.log(JSON.stringify(err, null, 2));
+    return browserDriver.sauceJobStatus(false);
   })
   .quit();