Fix tests for Windows

[mdedetrich]

Could be related to #112

When working on this PR the tests failed on windows CI because of

[info] JS should
[error]   x create JS objects from various types
[error]    '"\\path\\to\\file"' != '"/path/to/file"' (JsSpec.scala:16)
[error]   x create JS objects with implicit conversions
[error]    '"\\path\\to\\file"' != '"/path/to/file"' (JsSpec.scala:42)

Appears to be an issue with line separators on different platforms.