Following the advice of rubygems:

WARNING:  pessimistic dependency on refinerycms-core (~> 3.0.0) may be overly strict
  if refinerycms-core is semantically versioned, use:
    add_runtime_dependency 'refinerycms-core', '~> 3.0', '>= 3.0.0'
WARNING:  pessimistic dependency on friendly_id (~> 5.0.1) may be overly strict
  if friendly_id is semantically versioned, use:
    add_runtime_dependency 'friendly_id', '~> 5.0', '>= 5.0.1'
WARNING:  See http://guides.rubygems.org/specification-reference/ for help