Use twitter 5.9.0

Remove "$VERBOSE = nil" because the warning message doesn't appear.
Modify "Twitter.configure ..." to "client = Twitter::REST::Client ..."
(this is a new specification of Twitter gem).
Modify from "oauth_token" to "access_token" and from "oauth_token_secret" to
"access_token_secret".
Rescue the error which is thrown from client.update method.

ref.
  http://rdoc.info/gems/twitter/Twitter/REST/Client
  http://rdoc.info/gems/twitter/Twitter/REST/Tweets#update-instance_method
  http://rdoc.info/gems/twitter/Twitter/Error/Unauthorized
Modify README
Add an explanation about 4 tokens in trc.rb