BE review changes

app/models/blob.rb

@@ -63,7 +63,7 @@ class Blob < SimpleDelegator
   end
 
   def balsamiq?
-    binary? && extname.downcase.delete('.') == 'bmpr'
+    binary? && extension == 'bmpr'
   end
 
   def stl?

spec/features/projects/blobs/balsamiq_preview_spec.rb

@@ -7,7 +7,6 @@ feature 'Balsamiq preview', :feature, :js do
   let(:project) { create(:project) }
   let(:branch) { 'add-balsamiq-file' }
   let(:path) { 'files/images/balsamiq.bmpr' }
-  let(:file_content) { find('.file-content') }
 
   before do
     project.add_master(user)
@@ -16,7 +15,7 @@ feature 'Balsamiq preview', :feature, :js do
   end
 
   it 'should show a loading icon' do
-    expect(file_content).to have_selector('.loading')
+    expect(find('.file-content')).to have_selector('.loading')
   end
 
   it 'should show a viewer container' do