如题，使用xcode9.3后新建工程，然后初始化pod init，结果报错：
pod init
――― MARKDOWN TEMPLATE ――――――
### Command
```
/usr/local/bin/pod init
```
### Report
* What did you do?
* What did you expect to happen?
* What happened instead?
### Stack
```
CocoaPods : 1.3.1
Ruby : ruby 2.3.3p222 (2016-11-21 revision 56859) [universal.x86_64-darwin17]
RubyGems : 2.6.14
Host : Mac OS X 10.13.4 (17E202)
Xcode : 9.3 (9E145)
Git : git version 2.15.1 (Apple Git-101)
Ruby lib dir : /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib
Repositories : master - https://github.com/CocoaPods/Specs.git @ 8e9a8f04aa2579345661be7afc6f6fafdfb09d51
PrivatePods - https://github.com/ModulizationDemo/PrivatePods.git @ 22ad9a433c6e02afeef4d32da95ba0fe64799a0d
```
### Plugins
```
cocoapods-deintegrate : 1.0.1
cocoapods-plugins : 1.0.0
cocoapods-search : 1.0.0
cocoapods-stats : 1.0.0
cocoapods-trunk : 1.3.0
cocoapods-try : 1.1.0
```
### Error
```
RuntimeError - [Xcodeproj] Unknown object version.
/Library/Ruby/Gems/2.3.0/gems/xcodeproj-1.5.3/lib/xcodeproj/project.rb:217:in `initialize_from_file'
/Library/Ruby/Gems/2.3.0/gems/xcodeproj-1.5.3/lib/xcodeproj/project.rb:102:in `open'
/Library/Ruby/Gems/2.3.0/gems/cocoapods-1.3.1/lib/cocoapods/command/init.rb:41:in `validate!'
/Library/Ruby/Gems/2.3.0/gems/claide-1.0.2/lib/claide/command.rb:333:in `run'
/Library/Ruby/Gems/2.3.0/gems/cocoapods-1.3.1/lib/cocoapods/command.rb:52:in `run'
/Library/Ruby/Gems/2.3.0/gems/cocoapods-1.3.1/bin/pod:55:in `'
/usr/local/bin/pod:23:in `load'
/usr/local/bin/pod:23:in `'
```
――― TEMPLATE END ―――
'''
[!] Oh no, an error occurred.
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Looking for related issues on cocoapods/cocoapods...
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'''
可以看出是pod版本和xcode版本不兼容导致，所有要做pod升级
1.方案一 -- 失效
gem install cocoapods --pre
sudo gem install cocoapods --pre
2.方案二 -- 失效
gem update
sudo gem update
3.方案三 -- 成功
sudo gem update --system
sudo gem install -n /usr/local/bin cocoapods
