Test file paths are not recognized properly

Found in https://github.com/halohalospecial/atom-elmjutsu/issues/131#issuecomment-429499644

In Windows

• nodejs 8.12.0
• yarn 1.10.1
• elm-test@0.19.0-beta10, 0.19.0-beta11

These pattens do not work. Tested from PowerShell.

PS D:\Users\Romancer\workspace\elm-spa-example> elm-test make .\tests\RoutingTests.elm
-- NO INPUT --------------------------------------------------------------------

What should I make though? I need more information, like:

    elm make src/Main.elm
    elm make src/This.elm src/That.elm

However many files you give, I will create one JS file out of them.

PS D:\Users\Romancer\workspace\elm-spa-example> elm-test make D:\Users\Romancer\workspace\elm-spa-example\tests\RoutingTests.elm
-- NO INPUT --------------------------------------------------------------------

What should I make though? I need more information, like:

    elm make src/Main.elm
    elm make src/This.elm src/That.elm

However many files you give, I will create one JS file out of them.

This works:

PS D:\Users\Romancer\workspace\elm-spa-example> elm-test make tests\RoutingTests.elm

In Linux (Windows Subsystem of Linux, same machine)

• nodejs 8.11.4
• yarn 1.10.1
• elm-test@0.19.0-beta10, 0.19.0-beta11

Not works:

> elm-test make ./tests/RoutingTests.elm
-- NO INPUT --------------------------------------------------------------------

What should I make though? I need more information, like:

    elm make src/Main.elm
    elm make src/This.elm src/That.elm

However many files you give, I will create one JS file out of them.

Work:

> elm-test make tests/RoutingTests.elm

> elm-test make /mnt/d/Users/Romancer/workspace/elm-spa-example/tests/RoutingTests.elm

Start by reproducing the reported elm-test make commands in PowerShell and WSL, comparing relative paths with ./ and absolute Windows paths. Trace the CLI's file-argument handling; done means the listed Windows and Linux path forms are recognized consistently rather than reported as no input.