Merge pull request #10 from Vugario/with-header-return-this

withHeader method did not return the current instance.

src/Ixudra/Curl/Builder.php

@@ -116,6 +116,8 @@ class Builder {
     public function withHeader($header)
     {
         $this->curlOptions[ 'HTTPHEADER' ][] = $header;
+
+        return $this;
     }
 
     /**