Fix Sprockets 4 tests

Add required manifest files so we don't get exceptions.

In sprockets 4 when you render a `.scss` file it will give you the raw file instead of the generated CSS. To fix tests we must generate css instead of scss.

Author: schneems

test/fixtures/alternate_config_project/app/assets/config/manifest.js

@@ -0,0 +1,3 @@
+//= link_tree ./images
+//= link_directory ../javascripts .js
+//= link_directory ../stylesheets .css

test/fixtures/sass_project/app/assets/config/manifest.js

@@ -0,0 +1,3 @@
+//= link_tree ./images
+//= link_directory ../javascripts .js
+//= link_directory ../stylesheets .css

test/fixtures/scss_project/app/assets/config/manifest.js

@@ -0,0 +1,3 @@
+//= link_tree ./images
+//= link_directory ../javascripts .js
+//= link_directory ../stylesheets .css

test/sass_rails_test.rb

@@ -144,7 +144,7 @@ class SassRailsTest < Sass::Rails::TestCase
 
   test 'globbed imports work when new file is added' do
     project = 'scss_project'
-    filename = 'application.scss'
+    filename = 'application.css'
 
     within_rails_app(project) do |tmpdir|
       asset_output(filename)
@@ -161,7 +161,7 @@ class SassRailsTest < Sass::Rails::TestCase
 
   test 'globbed imports work when globbed file is changed' do
     project = 'scss_project'
-    filename = 'application.scss'
+    filename = 'application.css'
 
     within_rails_app(project) do |tmpdir|
       asset_output(filename)