fix typo (cancelled)

[nagamatu]

There is a typo in status.rb and cause an error for "cancelled" state:

$ travis logs --repo ethereum/go-ethereum 7542
displaying logs for ethereum/go-ethereum#7542.1
unknown state "cancelled" for #<Travis::Client::Job: ethereum/go-ethereum#7542.1>

[BanzaiMan]

I will point out that doubling l's is British. While it's not uniformly enforced, most of the existing documentation is American English.