refactor(Document.php): use PHP_EOL constant instead of "\n\n" string literal in paragraphs method

Author: kambo-1st

src/Docstore/Document.php

@@ -9,6 +9,8 @@
 use function strpos;
 use function count;
 
+use const PHP_EOL;
+
 /**
  * Interface for interacting with a document.
  */
@@ -44,7 +46,7 @@ public function __construct(
      */
     public function paragraphs(): array
     {
-        return explode("\n\n", $this->pageContent);
+        return explode(PHP_EOL . PHP_EOL, $this->pageContent);
     }
 
     /**