Fix #58 - Side by side diff shows empty diff

- Reverted used sample texts.

Author: DigiLive

example/example.php

@@ -11,8 +11,8 @@
 require '../vendor/autoload.php';
 
 // Include two sample files for comparison.
-$sampleA = file_get_contents(dirname(__FILE__) . '/c.txt');
-$sampleB = file_get_contents(dirname(__FILE__) . '/d.txt');
+$sampleA = file_get_contents(dirname(__FILE__) . '/a.txt');
+$sampleB = file_get_contents(dirname(__FILE__) . '/b.txt');
 
 // Options for generating the diff.
 $customOptions = [