Use square icon in MacOS dock

[alya]

To better align with MacOS design patterns, we should use a square Zulip icon in the Mac dock, instead of the circle icon we currently use: /static/images/logo/zulip-icon-square.svg.

CZO discussion

[spurjhattam2207]

@zulipbot claim

[zulipbot]

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[spurjhattam2207]

Apparently this has already been solved; on the zulip community chat I could see.

[zulipbot]

@spurjhattam2207 You have been unassigned from this issue because you have not made any updates for over 14 days. Please feel free to reclaim the issue if you decide to pick up again. Thanks!