prepare_deploy: report which download has failed

lib/tasks/docs.thor

@@ -244,12 +244,18 @@ class DocsCLI < Thor
           FileUtils.mkpath(dir)
 
           ['index.json', 'meta.json'].each do |filename|
-            open("https://docs.devdocs.io/#{doc.path}/#{filename}?#{time}") do |file|
+            json = "https://docs.devdocs.io/#{doc.path}/#{filename}?#{time}"
+            begin
+              open(json) do |file|
                 mutex.synchronize do
                   path = File.join(dir, filename)
                   File.write(path, file.read)
                 end
               end
+            rescue => e
+              puts "Docs -- Failed to download #{json}!"
+              throw e
+            end
           end
 
           puts "Docs -- Downloaded #{doc.slug}"