新增：文件blame 上个版本的行号

app/views/api/v1/projects/blame.json.jbuilder

@@ -16,6 +16,7 @@ json.blame_parts @result_object['blame_parts'] do |part|
     json.committed_time render_unix_time(part['commit']['committed_time'])
     json.created_time render_unix_time(part['commit']['created_time'])
   end
+  json.previous_number part['previous_number']
   json.current_number part['current_number']
   json.effect_line part['effect_line']
   json.lines part['lines']