Support for Ruby 2.4

[tmaszk]

After upgrading to Ruby 2.4, when using vim-kompleter I receive the warning message "... /vim-kompleter/ruby/kompleter.rb:217: warning: constant ::Fixnum is deprecated"

The issue is the Ruby is depricating Fixnum in favor of Integer, see Ruby 2.4 release notes

Steps to reproduce:

• run vim
• insert some text
• hit "esc" key
• see warning message

The warning message is annoying but doesn't affect the file being edited.