Update readme: listen_port is integer for Hiera

[AranVinkItility]

Pull Request (PR) description

Fix readme example for streamhosts using Hiera. It incorrectly states that listen_port is a string value when using hiera.

This Pull Request (PR) fixes the following issues

Using the example hiera data for streamhosts gives the following error:

[root@nginxlbmasters /]# puppet agent -t
Info: Using configured environment 'kubernetes'
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Retrieving locales
Info: Loading facts
Error: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Evaluation Error: Error while evaluating a Resource Statement, Nginx::Resource::Streamhost[kubernetes-api-streamhost]: parameter 'listen_port' expects an Integer value, got String (file: /etc/puppetlabs/code/environments/kubernetes/modules/nginx/manifests/init.pp, line: 181) on node nginxlbmasters.dkkiwezbbzwezjsuf2qq5optbd.ax.internal.cloudapp.net

[alexjfisher]

@AranVinkItility Thanks!