Updated sql-parser library.

Signed-off-by: Dan Ungureanu <udan1107@gmail.com>

libraries/sql-parser/src/UtfString.php

@@ -1,5 +1,17 @@
 <?php
 
+/**
+ * Implementation for UTF-8 strings.
+ *
+ * The subscript operator in PHP, when used with string will return a byte
+ * and not a character. Because in UTF-8 strings a character may occupy more
+ * than one byte, the subscript operator may return an invalid character.
+ *
+ * Because the lexer relies on the subscript operator this class had to be
+ * implemented.
+ *
+ * @package SqlParser
+ */
 namespace SqlParser;
 
 /**