[no-relative-parent-imports] support windows

[1pete]

make rule no-relative-parent-imports support windows

as you see, appveyor ci failed in master branch, i think because windows uses \ as a directory delimiter
so i change path check to use regular expression [\\/]

[coveralls]

Coverage remained the same at 97.284% when pulling 6920bb9 on 1pete:no-relative-parent-imports-windows into 5480240 on benmosher:master.

[coveralls]

Coverage remained the same at 97.284% when pulling 6920bb9 on 1pete:no-relative-parent-imports-windows into 5480240 on benmosher:master.

[coveralls]

Coverage remained the same at 97.284% when pulling 6920bb9 on 1pete:no-relative-parent-imports-windows into 5480240 on benmosher:master.

[coveralls]

Coverage remained the same at 97.284% when pulling 6920bb9 on 1pete:no-relative-parent-imports-windows into 5480240 on benmosher:master.

[ljharb]

I’m confused; resolvers should be abstracting away things like “windows uses backslash” from us

[benmosher]

@ljharb that is a great point but this PR implies we don't live in that universe--yet. 😄 fwiw I don't recall anything in any resolvers normalizing slashes. but that would be great to avoid stuff like this.

where "stuff like this" := intermittent AppVeyor gotchas.

thanks @1pete!