Highlighter::lineNumbers(): bug fix - remove stray blank line at end of output

The `lineNumbers()` functionality adds a new line marker at the end of each line, including the last line, meaning that any code snippets being passed through this function will have a stray blank line at the end of the output.

Fixed now.

Author: jrfnl

src/Highlighter.php

@@ -315,6 +315,6 @@ private function lineNumbers(array $lines, $markLine = null)
             $snippet .= $line . PHP_EOL;
         }
 
-        return $snippet;
+        return rtrim($snippet, PHP_EOL);
     }
 }