Set dist reference for root package as well, fixes #4828

src/Composer/Package/Loader/RootPackageLoader.php

@@ -84,12 +84,17 @@ class RootPackageLoader extends ArrayLoader
             }
 
             $config['version'] = $version;
-            if($commit){
+            if ($commit) {
                 $config['source'] = array(
                     'type' => '',
                     'url' => '',
                     'reference' => $commit
                 );
+                $config['dist'] = array(
+                    'type' => '',
+                    'url' => '',
+                    'reference' => $commit
+                );
             }
         }