When you encounter
/Users/kernel/.gem/ruby/2.0.0/gems/mysql2-0.3.16/lib/mysql2.rb:8:in
`require': dlopen(/Users/kernel/.gem/ruby/2.0.0/gems/mysql2-0.3.16/lib/mysql2/mysql2.bundle, 9):
Library not loaded:
/usr/local/lib/libmysqlclient.18.dylib (LoadError)
Try gem pristine mysql2
, this command restores installed gems to pristine condition from files located in the gem cache