Improve code

[dsh0416]

• Unify the 4 spaces tabs and 2 spaces tabs in all files
• Unify ruby code style with .rubocop definition
• Remove ambiguous method definition
• Remove incorrect attr_accessor definition in Qiniu::Logger
• Remove not recommended RSpec equal comparisions
• Add Ruby 2.5.0 to CI test as it has been published
• Reduce line count of some methods
• Remove useless %Q and %q

[jemygraw]

@dsh0416 听闻我merge了阁下pr被贴朋友圈示众，深感羞愧。感谢您给我的指导，以后我会更加用心一点。谢谢

[dsh0416]

没有没有，我本来是开玩笑的，没想到响应这么迅速 🤦‍♀️