Update jeweler for next release

[tessie]

@joschi I was trying to update the gem and then noticed that rake version etc was giving error

NoMethodError: undefined methoddependencies_for' for # Did you mean? dependencies /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler/specification.rb:73:in block in set_jeweler_defaults' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler/specification.rb:41:inchdir' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler/specification.rb:41:in set_jeweler_defaults' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler.rb:37:ininitialize' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler/tasks.rb:52:in new' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler/tasks.rb:52:injeweler' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/jeweler-2.1.1/lib/jeweler/tasks.rb:82:in block in define' /Users/tessy/.rvm/gems/ruby-2.4.1/gems/rake-12.1.0/exe/rake:27:in<top (required)>' /Users/tessy/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in eval' /Users/tessy/.rvm/gems/ruby-2.4.1/bin/ruby_executable_hooks:15:in

'`

But now it showing a warning with nokogiri. I think this could be merged .Once this is done I could do the jeweler release. I tried fixing it. Updating nokogiri to the latest version would break older ruby versions. Let me know know your suggestions

[milgner]

@tessie first things first: thank you for helping out! I'm really sorry I've been so unresponsive for so long, will try becoming more involved if necessary.

As for breaking compatibility with older versions, I think there are still people out there being stuck on Ruby 1.9. What do you think about making one last release with 1.9 support and then dropping support for pre-2.1 rubies?

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