im getting the following when i try running it:

C:/Ruby22-x64/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in require': cannot load such file -- rest-client (LoadError) from C:/Ruby22-x64/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:inrequire'
from bittrex_bot.rb:1:in

any advice?
thanks