Modify OS.isWindows to check platform before version

[alejzeis]

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Description

Previously OS.isWindows checked if the windows version matched the one required. This worked fine, except for the fact that it would end up comparing a linux kernel version to a windows version as it didn't check if the platform was Windows in the first place before.

This caused issues as it would throw an error when comparing with non-semver Linux kernels (such as Fedora). Tests would fail and notably the settings/preferences dialogs would fail to open. Now it checks if the current platform is Windows first, and if not, immediately returns false.

All tests pass now (previously on first checkout they failed on my system), and the preferences dialog successfully opens. No errors can be found in the console.

My OS is Fedora 28 x64.

Fixes: #2396

[scottnonnenberg-signal]

Hey there - thanks for this change! What happens if you run yarn format? This project (via that command and editor integration) use a code auto-formatter called prettier, and it makes it easier on all of us, since we don't have to give PR feedback about code formatting. :0)

[alejzeis]

Sorry about that, I ran yarn format and pushed the changes. I'm not sure if I'm supposed to squash the two commits so I just left them separate.