Move packagist check to a Haskell binary

lib/up2date.rb

@@ -77,12 +77,7 @@ module SlackBuilder
     end
 
     def latest
-      full_name = [@vendor, @name].join '/'
-      uri = URI "https://repo.packagist.org/p2/#{full_name}.json"
-      response = Net::HTTP.get uri, {
-        'content-type' => 'application/json'
-      }
-      JSON.parse(response)['packages'][full_name].first['version']
+      `./bin/slackbuilder #{@vendor} #{@name}`.strip
     end
   end