dev: rubocop rake task is no longer a prereq for test

- instead, make `rubocop` a prereq for `default`
- also make `compile` a preqreq for `default`
- and update the CI task to explicitly run the `rubocop` task

This was driven out by introducing TruffleRuby to CI, which doesn't
yet fully support rubocop.

Part of #2089

Rakefile

@@ -82,4 +82,8 @@ require_relative "tasks/docs-linkify"
 require_relative "tasks/rubocop"
 require_relative "tasks/set-version-to-timestamp"
 
+# work around Hoe's inflexibility about the default tasks
+Rake::Task[:default].prerequisites.unshift("compile")
+Rake::Task[:default].prerequisites.unshift("rubocop")
+
 # vim: syntax=Ruby

concourse/tasks/rake-test/run.sh

@@ -60,7 +60,7 @@ pushd nokogiri
 
   code-climate-setup
 
-  bundle exec rake compile ${test_task}
+  bundle exec rake rubocop compile ${test_task}
 
   code-climate-shipit
 

tasks/rubocop.rb

@@ -10,5 +10,3 @@
 task :rubocop_frozen_string_literals do
   sh "rubocop lib --auto-correct-all --only Style/FrozenStringLiteralComment"
 end
-
-task :test => :rubocop