Remove jasmine ruby gem and its requiring

This was missed from the pull request that
replaced the jasmine ruby gem with the
jasmine-browser-runner:

#382

Author: tombye

govuk_tech_docs.gemspec

@@ -25,6 +25,7 @@ Gem::Specification.new do |spec|
   files_in_git = `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
 
   # Include assets from GOV.UK Frontend library in the distributed gem
+  # Extra line
   govuk_frontend_assets = Dir["node_modules/govuk-frontend/**/*.{scss,js,mjs,woff,woff2,png,svg,ico}", "node_modules/govuk-frontend/dist/govuk/assets/manifest.json"]
 
   spec.files         = files_in_git + govuk_frontend_assets