Bump Arcanist client version to 3

Summary:
Thinking about this, I think it's worthwhile to bump versions for T1249/T1250.
The problem is that if you have an old Arcanist, trying to update diffs against
a new Phabricator will create new diffs instead, and it probably won't be
obvious what's wrong.

Bump the versions so users will get a message like "oh, hey, you should
upgrade".

Test Plan:
  - Tried to diff against a mismatched version.
  - Diffed against a matching version.

Reviewers: btrahan, jungejason, aran

Reviewed By: aran

CC: aran

Differential Revision: https://secure.phabricator.com/D1257

src/workflow/base/ArcanistBaseWorkflow.php

@@ -213,7 +213,7 @@ class ArcanistBaseWorkflow {
         'conduit.connect',
         array(
           'client'              => 'arc',
-          'clientVersion'       => 2,
+          'clientVersion'       => 3,
           'clientDescription'   => php_uname('n').':'.$description,
           'user'                => $user,
           'certificate'         => $certificate,