title: when install pod ,ERROR "Invalid `Podfile` file: undefined method `plateform'
body: <p>I'am a new ios develper, I need to install 'AFNetworking'.</p>
  
  <p>first, i have installed cocoapods;</p>
  
  <p>second, i created a 'Podfile' in my wordspace;</p>
  
  <pre><code>source 'https://github.com/CocoaPods/Specs.git'
  platform :ios, '8.0'
  pod 'AFNetworking'
  </code></pre>
  
  <p>then, i run
  <code>pod install</code>
  There is a ERROR:</p>
  
  <pre><code>/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/pathname.rb:422:in `open': No such file or directory - /Users/nemo/.cocoapods/repos (Errno::ENOENT)
  from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/pathname.rb:422:in `foreach'
  from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/pathname.rb:422:in `children'
  from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.35.0/lib/cocoapods/sources_manager.rb:63:in `all'
  from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.35.0/lib/cocoapods/user_interface/error_report.rb:130:in `repo_information'
  from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.35.0/lib/cocoapods/user_interface/error_report.rb:34:in `report'
  from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.35.0/lib/cocoapods/command.rb:58:in `report_error'
  from /Library/Ruby/Gems/2.0.0/gems/claide-0.7.0/lib/claide/command.rb:300:in `handle_exception'
  from /Library/Ruby/Gems/2.0.0/gems/claide-0.7.0/lib/claide/command.rb:274:in `rescue in run'
  from /Library/Ruby/Gems/2.0.0/gems/claide-0.7.0/lib/claide/command.rb:264:in `run'
  from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.35.0/lib/cocoapods/command.rb:45:in `run'
  from /Library/Ruby/Gems/2.0.0/gems/cocoapods-0.35.0/bin/pod:43:in `&lt;top (required)&gt;'
  from /usr/bin/pod:23:in `load'
  from /usr/bin/pod:23:in `&lt;main&gt;'
  </code></pre>