More env variables for travis build to fix coveralls (#583)

* Added TRAVIS_* env variables for coveralls.

* Add more environment variables inside docker-compose.ci.

TRAVIS and TRAVIS_PULL_REQUEST. First variable is important for node-coveralls.
See the code below:
  if (process.env.TRAVIS){
    options.service_name = 'travis-ci';
    options.service_job_id = process.env.TRAVIS_JOB_ID;
    options.service_pull_request = process.env.TRAVIS_PULL_REQUEST;
    git_commit = 'HEAD';
    git_branch = process.env.TRAVIS_BRANCH;
  }

docker-compose.ci.yml

@@ -9,5 +9,7 @@ services:
       network: host
     environment:
       COVERALLS_REPO_TOKEN:
+      TRAVIS:
       TRAVIS_JOB_ID:
       TRAVIS_BRANCH:
+      TRAVIS_PULL_REQUEST: