Download dev version of wordpress: (in terminal)
$ svn co http://develop.svn.wordpress.org/trunk/ wp-dev

Then use in gulpfile.js:
gulp.task( 'i18n', shell.task(
        'php /Users/ashokkumarnath/Desktop/pot/wp-dev/tools/i18n/makepot.php wp-plugin . lang/gtd.po'
));

/Users/ashokkumarnath/Desktop/pot/wp-dev/tools/i18n/makepot.php is the path to makepot.php file of downloaded wordpress