fix source parameter for signing key

This has been the case for a very long time:
puppetlabs/puppetlabs-apt@0f3bdcd

Author: shieldwed

manifests/repo/apt.pp

@@ -99,7 +99,7 @@
       repos        => 'main',
       key          => {
         id         => $repo_key_name,
-        key_source => $repo_key_source,
+        source     => $repo_key_source,
       },
       pin          => $priority,
       architecture => $arch,

spec/classes/repo_apt_spec.rb

@@ -61,7 +61,7 @@
             release: facts[:lsbdistcodename].to_s,
             key: {
               'id' => 'EED3351AFD72E5437C050F0388F6CDEE78FA6D97',
-              'key_source' => 'https://download.gluster.org/pub/gluster/glusterfs/4.1/rsa.pub'
+              'source' => 'https://download.gluster.org/pub/gluster/glusterfs/4.1/rsa.pub'
             },
             location: "https://download.gluster.org/pub/gluster/glusterfs/4.1/LATEST/Debian/#{facts[:lsbdistcodename]}/amd64/apt/"
           )
@@ -81,7 +81,7 @@
             release: facts[:lsbdistcodename].to_s,
             key: {
               'id' => '8B7C364430B66F0B084C0B0C55339A4C6A7BD8D4',
-              'key_source' => 'https://download.gluster.org/pub/gluster/glusterfs/3.12/rsa.pub'
+              'source' => 'https://download.gluster.org/pub/gluster/glusterfs/3.12/rsa.pub'
             },
             location: "https://download.gluster.org/pub/gluster/glusterfs/01.old-releases/3.12/LATEST/Debian/#{facts[:lsbdistcodename]}/amd64/apt/"
           )