Incorrect namespace in plugin after scaffolding

[kevinfodness]

Description of the bug

The namespace in the plugin is set to Alley\WP\[MySite]_Plugin instead of MySite_Plugin.

Steps To Reproduce

1. Run the configure script on this repo and give it some values.
2. Run composer phpcs and notice that WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedNamespaceFound error triggers because the namespace in the plugin starts with Alley\WP\ when it should not.

[kevinfodness]

Fixed by #178