Fix Composer script 'phplint'

Fixed:
- Syntax for multiple starting points
- Match only regular PHP files

Amends: da57afb

composer.json

@@ -63,7 +63,7 @@
             "@phpcs",
             "@phpunit"
         ],
-        "phplint": "find {src,tests} -name '*.php' -print0 | xargs -0 -n1 -P8 php -l | grep -v '^No syntax errors detected'; test $? -eq 1",
+        "phplint": "find src tests -type f -name '*.php' -print0 | xargs -0 -n1 -P8 php -l | grep -v '^No syntax errors detected'; test $? -eq 1",
         "phpcs": "php vendor/bin/phpcs -ps --colors src/ tests/",
         "phpcbf": "php vendor/bin/phpcbf -ps --colors src/ tests/",
         "phpunit": "php vendor/bin/phpunit --coverage-text"