Conditionally require faraday/multipart

Only Require Faraday Multipart if Faraday Version is greater than
2 because Faraday V1 includes the gem already.

#392

Author: ajGingrich

lib/openai.rb

@@ -1,5 +1,5 @@
 require "faraday"
-require "faraday/multipart"
+require 'faraday/multipart' if Gem::Version.new(Faraday::VERSION) >= Gem::Version.new('2.0')
 
 require_relative "openai/http"
 require_relative "openai/client"