[VarDumper] Fix dumped content type in CurlCasterTest

Author: alexandre-daubois

Tests/Caster/CurlCasterTest.php

@@ -31,7 +31,7 @@ public function testCastCurl()
             <<<'EODUMP'
 CurlHandle {
   url: "http://example.com/"
-  content_type: "text/html; charset=UTF-8"
+  content_type: "text/html"
   http_code: 200%A
 }
 EODUMP, $ch);