redis_exporter is downloaded every puppet run

[blupman]

Affected Puppet, Ruby, OS and module versions/distributions

Puppet: 4.10.10
Ruby: ruby 2.3.3p222
Distribution: debian/stretch
Module version: voxpupuli/puppet-prometheus master branch

How to reproduce (e.g Puppet code you use)

  prometheus::exporter { 'redis_exporter':
    port   => 9121t,
  }

What are you seeing

When useing redis_exporter, the download of the package is performed every puppet run:

Info: Applying configuration version 'production-0-g1e58a761'
Notice: /Stage[main]/Prometheus::Redis_exporter/Archive[/tmp/redis_exporter-0.11.2.tar.gz]/creates: creates changed 'archive not extracted' to 'extracting in /opt/redis_exporter-0.11.2.linux-amd64 to create /opt/prometheus::redis_exporter-0.11.2.linux-amd64/prometheus::redis_exporter'
Notice: Applied catalog in 4.96 seconds

I think this is caused by useing ${name} (=prometheus::redis_exporter) in stead of ${service_name} (=redis_exporter)

What behaviour did you expect instead

only once a download of of the redis_exporter

Output log

Any additional information you'd like to impart

I have created a small pull request to change this.