Change isGitIgnoredSync and isGitIgnored

[fisker]

Currently isGitIgnoredSync work like this

isGitIgnoredSync({cwd})(file)

and isGitIgnored work like this

(await isGitIgnored({}))(file);

// Note the following doesn't work
await isGitIgnored({})(file);

Let's change them to

isGitIgnoredSync(file, {cwd})

and

await isGitIgnored(file, {cwd});

[fisker]

I'll rethink about this #239 (comment)