add log file

src/post-receive.php

@@ -7,7 +7,9 @@ if ( $_SERVER['HTTP_X_GITHUB_EVENT'] == 'push' ) {
 
     if( ($fp = popen($command, "r")) ) {
         while( !feof($fp) ){
-            echo fread($fp, 1024);
+            $result = fread($fp, 1024);
+            file_put_contents("build.log", $result, FILE_APPEND);
+            echo $result;
             flush();
         }
         fclose($fp);