Tighten puppet_forge version range in r10k.gemspec

Co-authored-by: Tim Meusel <tim@bastelfreak.de>

r10k.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'cri', '>= 2.15.10'
   s.add_dependency 'log4r',     '1.1.10'
   s.add_dependency 'multi_json', '~> 1.10'
-  s.add_dependency 'puppet_forge', '>= 4.1.0'
+  s.add_dependency 'puppet_forge', '>= 4.1.0', '< 7'
   s.add_dependency 'gettext-setup', '>=0.24', '<2.0'
   s.add_dependency 'jwt', '>= 2.2.3', '< 3'
   s.add_dependency 'minitar', '>= 0.9', '< 2'