spec_helper: Extract FSF approval from wking.github.io/fsf-api

Ideally the FSF would be maintaining the API (or any API), but until
someone can talk them into that I think we can save work by
collaborating on the mock API.  Using a JSON API also allows us to
drop the Nokogiri dependency.

The parens feel excessive, and I'm not familiar with Ruby, so they
might be.  However, removing the parens from the libre check resulted
in:

  $ ./script/check-approval ISC
  ./script/check-approval:8:in `require_relative': /.../choosealicense.com/spec/spec_helper.rb:108: syntax error, unexpected tSTRING_BEG, expecting keyword_then or ';' or '\n' (SyntaxError)
  ...gs') && meta['tags'].include? 'libre'
  ...                               ^
  /.../choosealicense.com/spec/spec_helper.rb:116: syntax error, unexpected keyword_end, expecting end-of-input
          from ./script/check-approval:8:in `<main>'

Gemfile

@@ -17,7 +17,6 @@ end
 group :test do
   gem 'html-proofer', '~> 3.0'
   gem 'licensee'
-  gem 'nokogiri'
   gem 'rake'
   gem 'rspec'
   gem 'rubocop'

spec/spec_helper.rb

@@ -4,7 +4,6 @@ require 'jekyll'
 require 'json'
 require 'licensee'
 require 'open-uri'
-require 'nokogiri'
 
 module SpecHelper
   class << self
@@ -102,23 +101,15 @@ end
 
 def fsf_approved_licenses
   SpecHelper.fsf_approved_licenses ||= begin
-    url = 'https://www.gnu.org/licenses/license-list.en.html'
-    doc = Nokogiri::HTML(open(url).read)
-    list = doc.css('.green dt')
+    url = 'https://wking.github.io/fsf-api/licenses-full.json'
+    object = JSON.parse(open(url).read)
     licenses = {}
-    list.each do |license|
-      a = license.css('a').find { |link| !link.text.nil? && !link.text.empty? && link.attr('id') }
-      next if a.nil?
-      id = a.attr('id').downcase
-      name = a.text.strip
-      licenses[id] = name
+    object.each_value do |meta|
+      next unless (meta.include? 'identifiers') && (meta['identifiers'].include? 'spdx') && (meta.include? 'tags') && (meta['tags'].include? 'libre')
+      meta['identifiers']['spdx'].each do |identifier|
+        licenses[identifier.downcase] = meta['name']
+      end
     end
-
-    # FSF approved the Clear BSD, but doesn't use its SPDX ID or Name
-    if licenses.keys.include? 'clearbsd'
-      licenses['bsd-3-clause-clear'] = licenses['clearbsd']
-    end
-
     licenses
   end
 end