GoogleCode importer: Do not care about casing of image file extensions

Signed-off-by: Sven Strickroth <email@cs-ware.de>

lib/gitlab/google_code_import/importer.rb

@@ -327,7 +327,7 @@ module Gitlab
           link = "https://storage.googleapis.com/google-code-attachments/#{@repo.name}/issue-#{issue_id}/comment-#{comment_id}/#{filename}"
           
           text = "[#{filename}](#{link})"
-          text = "!#{text}" if filename =~ /\.(png|jpg|jpeg|gif|bmp|tiff)\z/
+          text = "!#{text}" if filename =~ /\.(png|jpg|jpeg|gif|bmp|tiff)\z/i
           text
         end.compact
       end

spec/fixtures/GoogleCodeProjectHosting.json

@@ -382,6 +382,11 @@
               "fileName" : "screenshot.png",
               "fileSize" : 0,
               "mimetype" : "image/png"
+            }, {
+              "attachmentId" : "001",
+              "fileName" : "screenshot1.PNG",
+              "fileSize" : 0,
+              "mimetype" : "image/x-png"
             } ]
           }, {
             "id" : 1,

spec/lib/gitlab/google_code_import/importer_spec.rb

@@ -65,6 +65,7 @@ describe Gitlab::GoogleCodeImport::Importer do
       expect(issue.description).to include('all the best!')
       expect(issue.description).to include('[tint2_task_scrolling.diff](https://storage.googleapis.com/google-code-attachments/tint2/issue-169/comment-0/tint2_task_scrolling.diff)')
       expect(issue.description).to include('![screenshot.png](https://storage.googleapis.com/google-code-attachments/tint2/issue-169/comment-0/screenshot.png)')
+      expect(issue.description).to include('![screenshot1.PNG](https://storage.googleapis.com/google-code-attachments/tint2/issue-169/comment-0/screenshot1.PNG)')
     end
 
     it "imports issue comments" do