Switch rubocop task to execute after the tests

When you're developing, you're testing and haven't yet settled on the
final state of the code so rubocop telling you you have some extra
spaces somewhere when you're trying to run the test suite is not very
useful.

Instead, let's run the specs first and rubocop afterwards.

Author: ivoanjo

Rakefile

@@ -38,4 +38,4 @@ end
 require 'rubocop/rake_task'
 RuboCop::RakeTask.new(:rubocop)
 
-task default: [:rubocop, :test, :spinach]
+task default: [:test, :spinach, :rubocop]