Specify minimum required ruby version

[Shalmezad]

Tried installing this in an old ruby instance, as expected it didn't work because it's using the new hash syntax:

SyntaxError: /usr/local/rvm/gems/ree-1.8.7-2012.02/gems/lograge-0.3.6/lib/lograge/formatters/graylog2.rb:9: odd number list for Hash
          short_message: short_message(data_clone)
                        ^
/usr/local/rvm/gems/ree-1.8.7-2012.02/gems/lograge-0.3.6/lib/lograge/formatters/graylog2.rb:9: syntax error, unexpected ':', expecting '}'
          short_message: short_message(data_clone)

Would recommend specifying a minimum version of ruby in the gem specification using something like spec.required_ruby_version = '>= 1.9.0'

https://ruby-doc.org/stdlib-2.2.3/libdoc/rubygems/rdoc/Gem/Specification.html#method-i-required_ruby_version-3D