dev/core#1393 - distmaker - Skip new file "vendor/bin/pscss"

dev/core#1393 - distmaker - Skip new file "vendor/bin/pscss"

This file was recently added by way of `scssphp`.  We don't use it, and
trying to bundle the symlink into the tarball breaks some consumers.

* Before (last release): `vendor/bin/pscss` does not exist
* Before (current master): `vendor/bin/pscss` is created as symlink, copied to tarball
* After (this commit): `vendor/bin/pscss` is created on dev-builds but omitted from tarball