Bump version to 1.7.3 in asset files and update version in index.js

Author: soderlind

build/index.asset.php

@@ -1 +1 @@
-<?php return array('dependencies' => array('wp-api-fetch', 'wp-i18n'), 'version' => '9e5c51f6474ac97c1f9d');
+<?php return array('dependencies' => array('wp-api-fetch', 'wp-i18n'), 'version' => '6df7975b628e4eda2261');