Merge pull request #613 from equalizedigital/william/604/prevent-0th-…

…displaying-on-readability-when-checkable-content--is-empty

When readability score is 0 use `N/A` instead of `0th`

includes/classes/class-summary-generator.php

@@ -291,7 +291,7 @@ private function calculate_content_grade() {
 			);
 		}
 
-		return $content_grade;
+		return (int) round( $content_grade );
 	}
 
 	/**