[v1.8.0-rc3] os.icns is outdated

[jmarrec]

Issue overview

Current Behavior

Possible Solution

Update the os.icns to match the new icon.

Details

Environment

Some additional details about your environment for this issue (if relevant):

• Platform (Operating system, version): macOS
• Version of OpenStudioApplication (if using an intermediate build, include SHA): v1.8.0-rc3

Context

• v1.8.0-rc3 Testing: Call for help from the community #743