Update dependency versioning

[gaganawhad]

WARNING:  open-ended dependency on safe_yaml (>= 0) is not recommended
  if safe_yaml is semantically versioned, use:
    add_runtime_dependency 'safe_yaml', '~> 0'
WARNING:  open-ended dependency on rspec (>= 0, development) is not recommended
  if rspec is semantically versioned, use:
    add_development_dependency 'rspec', '~> 0'
WARNING:  open-ended dependency on rubocop (>= 0, development) is not recommended
  if rubocop is semantically versioned, use:
    add_development_dependency 'rubocop', '~> 0'
WARNING:  open-ended dependency on byebug (>= 0, development) is not recommended
  if byebug is semantically versioned, use:
    add_development_dependency 'byebug', '~> 0'