check if file exists case-sensitive

[andyqier88]

when i use like below, the results are true

import { pathExists } from 'path-exists';

console.log(await pathExists('./readme.md')); // true
console.log(await pathExists('./README.md')); // true

in my boundary-judgment fileExistsWithCaseSync based on check-if-file-exists-case-sensitive

[sindresorhus]

If the file system is case-insensitive, the above behavior is correct. I don't think this package should work around that. Even a valid need for this is quite niche, so I'm going to pass on adding an option for it.