Merge branch 'unify-image_lazy_load_filter_spec.rb' into 'master'

Unify spec/lib/banzai/filter/image_lazy_load_filter_spec.rb

See merge request gitlab-org/gitlab-ce!19836

spec/lib/banzai/filter/image_lazy_load_filter_spec.rb

 require 'spec_helper'
-describe Banzai::Filter::ImageLazyLoadFilter, lib: true do
+describe Banzai::Filter::ImageLazyLoadFilter do
   include FilterSpecHelper
   def image(path)