Fix call for package upgradeable check and bring back the squirrel

Currently, the squirrel octicon is not shown in the packages list for packages which can be upgraded. This change brings back the squirrel by fixing a check for the `canUpgrade` call which sets the required class. (See: https://github.com/atom/settings-view/commit/2f866b464c2b8ee1487afcce78c785b5b12a0cf0 for related changes)

Before:

![screen shot 2014-08-16 at 10 43 08 pm](https://cloud.githubusercontent.com/assets/38924/3943055/00dc14e6-2586-11e4-8166-82701c795448.png)

After:

![screen shot 2014-08-16 at 10 20 46 pm](https://cloud.githubusercontent.com/assets/38924/3942987/d9c8890a-2582-11e4-9f9c-499eaa0280c3.png)

cc @kevinsawicki