```ruby
# -*- encoding: utf-8 -*-
$:.push File.expand_path("../lib", __FILE__)
require "sourcify/version"

Gem::Specification.new do |s|
  s.name        = "sourcify"
  s.version     = Sourcify::VERSION
  s.platform    = Gem::Platform::RUBY
  s.authors     = ["NgTzeYang"]
  s.email       = ["ngty77@gmail.com"]
  s.homepage    = "http://github.com/ngty/sourcify"
  s.summary     = %q{Workarounds before ruby-core officially supports Proc#to_source (& friends)}
  s.description = %q{}

  s.add_dependency 'ruby2ruby', '>= 1.2.5'
  s.add_dependency 'sexp_processor', '>= 3.0.5'
  s.add_dependency 'ruby_parser', '>= 2.0.5'
  s.add_dependency 'file-tail', '>= 1.0.5'

  # ParseTree (better performance + dynamic goodness, but not supported on java & 1.9.*)
  # Mandatory for 1.8.6, but optional for 1.8.7 onwards
  # gem.add_dependency "ParseTree", ">= 3.0.6"

  s.add_development_dependency 'bacon'

  s.files         = `git ls-files`.split("\n")
  s.test_files    = `git ls-files -- spec/*`.split("\n")
  s.require_paths = ["lib"]
end
```

Add ParseTree as a dependency for 1.8.6.
user
```ruby
# -*- encoding: utf-8 -*-
$:.push File.expand_path("../lib", __FILE__)
require "sourcify/version"

Gem::Specification.new do |s|
  s.name        = "sourcify"
  s.version     = Sourcify::VERSION
  s.platform    = Gem::Platform::RUBY
  s.authors     = ["NgTzeYang"]
  s.email       = ["ngty77@gmail.com"]
  s.homepage    = "http://github.com/ngty/sourcify"
  s.summary     = %q{Workarounds before ruby-core officially supports Proc#to_source (& friends)}
  s.description = %q{}

  s.add_dependency 'ruby2ruby', '>= 1.2.5'
  s.add_dependency 'sexp_processor', '>= 3.0.5'
  s.add_dependency 'ruby_parser', '>= 2.0.5'
  s.add_dependency 'file-tail', '>= 1.0.5'
  s.add_development_dependency 'bacon'

  # ParseTree (better performance + dynamic goodness, but not supported on java & 1.9.*)
  # Mandatory for 1.8.6, but optional for 1.8.7 onwards
  if RUBY_VERSION.include?('1.8.6')
    s.add_dependency "ParseTree", ">= 3.0.6"
  end

  s.files         = `git ls-files`.split("\n")
  s.test_files    = `git ls-files -- spec/*`.split("\n")
  s.require_paths = ["lib"]
end
```
assistant