Update QA to Chemlab 0.8

What does this MR do and why?

Updates qa/Gemfile to include Chemlab version 0.8.

Chemlab version 0.8+ introduced the ability to configure base_url's. Since chemlab-library-gitlab is built from chemlab-library-gitlab.gemspec, this will allow dependent projects to configure a Base URL.

Before

Given:

# spec_helper.rb
Chemlab.configure do |chemlab|
  chemlab.base_url = 'https://example.com'
end

# page.rb
module App
  class Page < Chemlab::Page
    path '/test'
  end
end

# test_spec.rb
Page.perform do |page|
  page.visit #=> Navigates to https://example.com/test
end

After

Given:

# spec_helper.rb
Chemlab.configure do |chemlab|
  App.base_url = 'https://another.example.com'
  chemlab.base_url = 'https://example.com'
end

# page.rb
module App
  include Chemlab::Library
  class Page < Chemlab::Page
    path '/test'
  end
end

# test_spec.rb
Page.perform do |page|
  page.visit #=> Navigates to https://another.example.com/test
end

This allows Chemlab to have several different applications configured separately. This will be useful for when GitLab needs to have a base URL that is separate from Chemlab's base URL.

MR acceptance checklist

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