Verify FileResourceStore on Windows

[joachimvh]

Currently all FileResourceStore tests work on Windows, due to the usage of path.posix, as was fixed in b489d69, but I should have a deeper look to see if it actually works when writing real files.

[RubenVerborgh]

Also https://docs.travis-ci.com/user/reference/windows/

[joachimvh]

Tests in #154 also work on Windows so this is resolved.

I tried adding Windows to travis but the builds seem to get stuck after finishing (example here).

Done. Your build exited with 0.

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.

Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#build-times-out-because-no-output-was-received

The build has been terminated

This might be because of the validation script that sets up a server and maybe doesn't close correctly on windows, but as long as it is this easy for it to get stuck I wouldn't rely on it for testing (especially since it doubles the amount of tests for travis and they take quite a bit longer than the linux tests).