Fix duplicated result when using globstar

[jopemachine]

Fixes #175.

I updated createFilterFunction using normalized path string instead of just path.

So, the below code lines return the commented values instead of [ 'a/b', './a/b' ].

// below code returns [ './a/b' ]
console.log(globbySync(['./a/**', './a']));

// below code returns [ 'a/b' ]
console.log(globbySync(['./a', './a/**']));

[sindresorhus]

Can you add a test?

[jopemachine]

Can you add a test?

Sure, I just made a test about this. Would this test be enough to test this case?