Replacing DIRECTORY_SEPARATOR with PHPCR seperator '/' because DIRECTORY...

..._SEPARATOR in windows is '\'

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | 
| Fixed tickets | 
| License       | MIT
| Doc PR        |