Fix copy text for robots.txt viewer (#464)

HealthCheck/Tools/class-health-check-robotstxt.php

@@ -18,7 +18,7 @@ class Health_Check_Robotstxt extends Health_Check_Tool {
 
 	public function __construct() {
 		$this->label       = __( 'robots.txt Viewer', 'health-check' );
-		$this->description = __( 'The <code>robots.txt</code> file tells search engines which folders are allowed to crawl and which not. WordPress generates a virtual files if there is no physical file. If there is a non-virtual file, the content is shown here.', 'health-check' );
+		$this->description = __( 'The <code>robots.txt</code> file tells search engines which directories are allowed to be crawled and which not. WordPress generates a virtual file if there is no physical file. If there is a non-virtual file, the content will be displayed here.', 'health-check' );
 
 		parent::__construct();
 	}