updated correctIndexOffset() to use mb_substr with encoding instead of just substr, added test to cover bug

Author: cmgmyr

src/TextFormatter.php

@@ -170,7 +170,7 @@ protected function getWordIndex($word, $offset)
      */
     protected function correctIndexOffset($index)
     {
-        return mb_strlen(substr($this->title, 0, $index), $this->encoding);
+        return mb_strlen(mb_substr($this->title, 0, $index, $this->encoding), $this->encoding);
     }
 
     /**

tests/TextFormatterTest.php

@@ -105,6 +105,11 @@ class TextFormatterTest extends TestCase
             'title' => 'test',
             'correct' => 'Test'
         ],
+        [
+            // tests for a bug with special characters
+            'title' => 'get up and dance — 7 reasons why you should be… moving your feet to the beat',
+            'correct' => 'Get Up and Dance — 7 Reasons Why You Should Be… Moving Your Feet to the Beat'
+        ],
     ];
 
     /** @test */