Gemfile

source "https://rubygems.org"

gem "octokit", "~> 4.0"

status.rb

require 'octokit'

Octokit.configure do |c|
  # create a token here https://github.com/settings/tokens/new
  c.access_token = '...'
end

# replace this with your repo and .travis.yml sha
repo = 'igorwwwwwwwwwwwwwwwwwwww/hello-world'
travis_yml_sha = '3063d5f6554f4d3470a62249e69788fc1e289c69'

prs = Octokit.pull_requests(repo, state: 'open')
prs.each do |pr|
  tree = Octokit.tree(repo, pr.head.sha)
  blob = tree.tree.find do |f| f.type == 'blob' && f.path == '.travis.yml' end
  if blob.sha == travis_yml_sha
    Octokit.create_status(repo, pr.head.sha, 'success', {
      context: 'travis-yml-modified',
      description: '.travis.yml is intact'
    })
  else
    Octokit.create_status(repo, pr.head.sha, 'failure', {
      context: 'travis-yml-modified',
      description: '.travis.yml was modified!'
    })
  end
end