fix failing test, read file from correct path

Author: manusajith

lib/generators/backbone/install/install_generator.rb

@@ -16,7 +16,7 @@ def inject_backbone
         # for JavaScript application.js manifest:        
         if File.exists? "#{Rails.root}/app/assets/javascripts/application.js"
           #add backbone.js files above the require_tree if present
-          if File.readlines("app/assets/javascripts/application.js").grep(/require_tree/).any?
+          if File.readlines("#{Rails.root}/app/assets/javascripts/application.js").grep(/require_tree/).any?
             inject_into_file "app/assets/javascripts/application.js", before: '//= require_tree .' do
               "//= require underscore\n//= require backbone\n//= require backbone_rails_sync\n//= require backbone_datalink\n//= require backbone/#{application_name.underscore}\n"
             end 
@@ -28,7 +28,7 @@ def inject_backbone
         # ...or for CoffeeScript application.js.coffee manifest:
         elsif File.exists? "#{Rails.root}/app/assets/javascripts/application.js.coffee" 
           #add backbone.js files above the require_tree if present
-          if File.readlines("app/assets/javascripts/application.js").grep(/require_tree/).any?
+          if File.readlines("#{Rails.root}/app/assets/javascripts/application.js").grep(/require_tree/).any?
             inject_into_file "app/assets/javascripts/application.js.coffee", before: '#= require_tree .' do
               "\n#= require underscore\n#= require backbone\n#= require backbone_rails_sync\n#= require backbone_datalink\n#= require backbone/#{application_name.underscore}\n"
             end