bugfix: get puppet version in gemfile from ENV: PUPPET_VERSION

in travis the configuration points to PUPPET_VERSION, instead of PUPPET_GEM_VERSION. I had decided for the slightly shorter but then missed it in the Gemfile configuration. This is fixed now

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
ignore failures for puppet 3.0 on ruby 2.0+

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
remove travis support for puppet 3.4, add puppet 3.6

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
fix incorrect variable reference for travis exclude

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
Merge pull request #30 from TelekomLabs/fix/gemfile_puppet

bugfix: get puppet version in gemfile from ENV: PUPPET_VERSION