Update my_activity.py to use crrev.com short URLs for Gerrit.

This causes review links to be shown using crrev.com/c/ or crrev.com/i/,
which are the ones recommended at https://polygerrit.appspot.com/.
This gerrit server is no longer used only by CrOS.

Change-Id: Ie6b856390ec465f9d35a5035547f7b779392b24c
Reviewed-on: https://chromium-review.googlesource.com/526612
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>

my_activity.py

@@ -95,11 +95,11 @@ rietveld_instances = [
 gerrit_instances = [
   {
     'url': 'chromium-review.googlesource.com',
-    'shorturl': 'crosreview.com',
+    'shorturl': 'crrev.com/c',
   },
   {
     'url': 'chrome-internal-review.googlesource.com',
-    'shorturl': 'crosreview.com/i',
+    'shorturl': 'crrev.com/i',
   },
   {
     'url': 'android-review.googlesource.com',