Ruby gems deprecation warning: Gem::Specification#has_rdoc= is deprecated with no replacement

$ gem build thrift.gemspec 
NOTE: Gem::Specification#has_rdoc= is deprecated with no replacement. It will be removed in Rubygems 4
Gem::Specification#has_rdoc= called from thrift.gemspec:15.
WARNING:  open-ended dependency on bundler (>= 1.11, development) is not recommended
  if bundler is semantically versioned, use:
    add_development_dependency 'bundler', '~> 1.11'
WARNING:  rubyforge_project= is deprecated and ignored. Please remove this from your gemspec to ensure that your gem continues to build in the future.
WARNING:  See https://guides.rubygems.org/specification-reference/ for help