Minor bug: app doesn't retain monitor affinity on relaunch

[jessegallagher]

When closing and relaunching the app on a multi-monitor system, the Spotify window retains its X/Y coordinates, but not which monitor it was on. So, for example, I keep the app in the top-right corner of my second monitor; on relaunch, it appears in the same position but on the main monitor.

This is using macOS 10.13.1 and Spotify 1.0.67.582.g19436fa3 on a Late-2014 5K iMac.