Update Parsedown.php

This solves a bug which stops referenced links formatting correctly when a space is inserted before a reference to a link right after a list.

This is caused because parsedown think's it's a secondary list rather, so it jumps to the next line.

Here is an example:

    + [Google][2]
    + [Youtube][1]  

      [1]: http://youtube.com
      [2]: http://google.com

Parsedown.php

@@ -182,7 +182,7 @@ class Parsedown
 
 				if (isset($element['interrupted']))
 				{
-					if ($line[0] === ' ')
+					if ($line[0] === ' ' and ! preg_match('/^[ ]{0,4}\[(.+?)\]:[ ]*([^ ]+)/', $line))
 					{
 						$element['lines'] []= '';
 
@@ -692,4 +692,4 @@ class Parsedown
 
 		return $text;
 	}
-}
+}