Remove unneeded dependency on electrical/file_concat module

[ghost]

This addresses #160

[solarkennedy]

can you adjust .fixtures.yml as well?

[ghost]

.fixtures.yml already has it commented out:

$ cat .fixtures.yml
fixtures:
  forge_modules:
    stdlib: "puppetlabs/stdlib"
    concat: "puppetlabs/concat"
#    file_concat: "git://github.com/electrical/puppet-lib-file_concat.git"
  symlinks:
    dns: "#{source_dir}"

[solarkennedy]

Thanks!