Composer incorrectly resolving paths on Windows

[noonanwebgroup]

Hey there, firstly thanks for this awesome package! I installed it, generated an example block and field as per the docs and I didn't see it being registered on the site. I spent a couple of hours scratching my head and wondered what I was doing wrong. I checked out the docs multiple times to see if there was something I was missing, but apparently not.

As I jumped into the source code, I realised that the composer was incorrectly resolving the path for Windows. It seems as though AcfComposer.php:95 is the issue. Rather than searching for the string '/' you could replace it with DIRECTORY_SEPARATOR to get the correct separator for that OS. After changing it, blocks and fields were registering perfectly.

[noonanwebgroup]

I've opened a pull request with the fix #72