Fix rubocop offense

Signed-off-by: Emily Casey <[email protected]>

Author: ekcasey

rakelib/dependency_cache_task.rb

@@ -111,7 +111,7 @@ def cache_task(uri)
     def component_ids
       conf = configuration('components').values.flatten.map { |component| component.split('::').last.snake_case }
       offline_cache = ENV['ADD_TO_CACHE']
-      if !offline_cache.nil?
+      unless offline_cache.nil?
         offline_cache = offline_cache.split(',')
         (conf << offline_cache).flatten!.uniq!
       end