Pin apt in fixtures until we depreciate puppet 4 support

Author: edestecd

.fixtures.yml

@@ -4,8 +4,12 @@ fixtures:
     stdlib: 'git://github.com/puppetlabs/puppetlabs-stdlib.git'
     postgresql: 'git://github.com/puppetlabs/puppet-postgresql.git'
     firewall: 'git://github.com/puppetlabs/puppetlabs-firewall.git'
-    apt: 'git://github.com/puppetlabs/puppetlabs-apt.git'
-    concat: 'git://github.com/puppetlabs/puppetlabs-concat.git'
+    apt:
+      repo: 'git://github.com/puppetlabs/puppetlabs-apt.git'
+      ref: '2.4.0'
+    concat:
+      repo: 'git://github.com/puppetlabs/puppetlabs-concat.git'
+      ref: '2.2.1'
     file_concat: 'git://github.com/electrical/puppet-lib-file_concat.git'
   symlinks:
     puppetdb: '#{source_dir}'