Fix route part in developer manual

[sualko]

In https://github.com/nextcloud/documentation/blob/master/developer_manual/app/routes.rst the example uses 'verb' => 'GET', but in the following list of possible values it's method. While verb is working quite fine, I assume this is just a typo.

[juliusknorr]

@sualko Would you mind to open a PR for that to fix? That would be great.