```ruby
# frozen_string_literal: true

lib = File.expand_path("../lib", __FILE__)
$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
require "jekyll/invoice/version"

Gem::Specification.new do |spec|
  spec.name          = "jekyll-invoice"
  spec.version       = Jekyll::Invoice::VERSION
  spec.authors       = ["Mark H. Wilkinson"]
  spec.email         = ["mhw@dangerous-techniques.com"]
  spec.summary       = "Produce invoices with Jekyll"
  spec.description   = "A collection of Jekyll plugins and conventions to produce nice HTML invoices."
  spec.homepage      = "http://github.com/mhw/jekyll-invoice"
  spec.license       = "MIT"

  spec.files         = `git ls-files -z`.split("\x0")
  spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
  spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
  spec.require_paths = ["lib"]

  spec.add_runtime_dependency "jekyll", "~> 3.3.0"

  spec.add_development_dependency "bundler", "~> 1.5"
  spec.add_development_dependency "rake"
  spec.add_development_dependency "minitest", "~> 5.0"
end
```

Update bundler requirement from ~> 1.5 to ~> 2.0
user
```ruby
# frozen_string_literal: true

lib = File.expand_path("../lib", __FILE__)
$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
require "jekyll/invoice/version"

Gem::Specification.new do |spec|
  spec.name          = "jekyll-invoice"
  spec.version       = Jekyll::Invoice::VERSION
  spec.authors       = ["Mark H. Wilkinson"]
  spec.email         = ["mhw@dangerous-techniques.com"]
  spec.summary       = "Produce invoices with Jekyll"
  spec.description   = "A collection of Jekyll plugins and conventions to produce nice HTML invoices."
  spec.homepage      = "http://github.com/mhw/jekyll-invoice"
  spec.license       = "MIT"

  spec.files         = `git ls-files -z`.split("\x0")
  spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }
  spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
  spec.require_paths = ["lib"]

  spec.add_runtime_dependency "jekyll", "~> 3.3.0"

  spec.add_development_dependency "bundler", "~> 2.0"
  spec.add_development_dependency "rake"
  spec.add_development_dependency "minitest", "~> 5.0"
end
```
assistant