title: Ruby Error in cocoa pods After upgrading os and installing xcode
body: <p>I got the following error when i run terminal command </p>
  
  <p><code>pod install</code> 
  command in terminal    </p>
  
  <pre><code>/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- rubygems/core_ext/kernel_warn (LoadError)
          from /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
          from /Library/Ruby/Site/2.3.0/rubygems.rb:1395:in `&lt;top (required)&gt;'
          from &lt;internal:gem_prelude&gt;:4:in `require'
          from &lt;internal:gem_prelude&gt;:4:in `&lt;internal:gem_prelude&gt;'
  
  JAYDEEPs-Mini:~ jaydeepvyas$ rvm -v
  rvm 1.29.6 (latest) by Michal Papis, Piotr Kuczynski, Wayne E. Seguin [https://rvm.io]
  
  JAYDEEPs-Mini:~ jaydeepvyas$ ruby -v
  ruby 2.3.7p456 (2018-03-28 revision 63024) [universal.x86_64-darwin18]
  JAYDEEPs-Mini:~ jaydeepvyas$ 
  </code></pre>