[5.4] Fixed Filesystem::files bug

[thetomcake]

Filesystem::files uses glob($directory.'/*');

On Windows this returns a / rather than a \ on the last directory separator and seems to be an oddity in the php core glob() function.

Example using glob($directory.'/*');

>>> $path = 'C:\filestest';
>>> File::files($path)
=> [
     "C:\filestest/testfile1.txt",
     "C:\filestest/testfile2.txt",
     "C:\filestest/testfile3.txt",
   ]

Example using glob($directory.DIRECTORY_SEPARATOR.'*');

>>> $path = 'C:\filestest';
>>> File::files($path)
=> [
     "C:\filestest\testfile1.txt",
     "C:\filestest\testfile2.txt",
     "C:\filestest\testfile3.txt",
   ]