add back in $apiVersion to make it easier to handle preview versions in the future

there are no preview versions now so checking against an empty array
also had to fix the acceptHeaderValue to correctly use the variable

Author: bobeagan

lib/Github/Api/PullRequest.php

@@ -22,11 +22,16 @@ class PullRequest extends AbstractApi
      *
      * @link https://developer.github.com/v3/pulls/#custom-media-types
      * @param string|null $bodyType
+     * @param string|null $apiVersion
      *
      * @return self
      */
-    public function configure($bodyType = null)
+    public function configure($bodyType = null, $apiVersion = null)
     {
+        if (!in_array($apiVersion, array())) {
+            $apiVersion = $this->client->getApiVersion();
+        }
+
         if (!in_array($bodyType, array('text', 'html', 'full', 'diff', 'patch'))) {
             $bodyType = 'raw';
         }
@@ -35,7 +40,7 @@ public function configure($bodyType = null)
             $bodyType .= '+json';
         }
 
-        $this->acceptHeaderValue = sprintf('application/vnd.github.%s.%s', $this->client->getApiVersion(), $bodyType);
+        $this->acceptHeaderValue = sprintf('application/vnd.github.%s.%s', $apiVersion, $bodyType);
 
         return $this;
     }