Merge pull request #788 from hkiciy/fix-deprecated

Accessing string offsets using curly braces has been deprecated in PHP 7.4.

src/SignatureMethod.php

@@ -58,7 +58,7 @@ public function checkSignature(Request $request, Consumer $consumer, Token $toke
         // Avoid a timing leak with a (hopefully) time insensitive compare
         $result = 0;
         for ($i = 0; $i < strlen($signature); $i++) {
-            $result |= ord($built{$i}) ^ ord($signature{$i});
+            $result |= ord($built[$i]) ^ ord($signature[$i]);
         }
 
         return $result == 0;