Add assets precompile hook

Finishes #11

lib/ember-cli/helpers.rb

@@ -14,5 +14,15 @@ def which(cmd)
 
       nil
     end
+
+    def override_assets_precompile_task!
+      Rake.application.instance_eval do
+        @tasks["assets:precompile:original"] = @tasks.delete("assets:precompile")
+        Rake::Task.define_task "assets:precompile", %i[assets precompile] => :environment do
+          EmberCLI.compile!
+          Rake::Task["assets:precompile:original"].execute
+        end
+      end
+    end
   end
 end

lib/ember-cli/railtie.rb

@@ -14,6 +14,10 @@ class Railtie < Rails::Railtie
       EmberCLI.enable! if non_production?
     end
 
+    rake_tasks do
+      require "ember-cli/rake_task"
+    end
+
     def non_production?
       !Rails.env.production? && Rails.configuration.consider_all_requests_local
     end

lib/ember-cli/rake_task.rb

@@ -0,0 +1,3 @@
+require "sprockets/rails/task"
+
+EmberCLI::Helpers.override_assets_precompile_task!