Fix distinct type query for tasks

When we were doing this same query in Postgres we were receiving
errors. This should address that problem.

Author: MichaelCrawfordNava

app/controllers/flex/tasks_controller.rb

@@ -11,8 +11,8 @@ def task_class
     end
 
     def index
+      @task_types = Flex::Task.distinct(:type).unscope(:order).pluck(:type)
       @tasks = filter_tasks
-      @task_types = task_class.distinct.pluck(:type)
     end
 
     def show