chore: Add comments on .travis.yml

Fix #11

Author: pvdlg

.travis.yml

@@ -1,16 +1,25 @@
 language: node_js
 node_js:
   - 8
+
+# Trigger a push build on master and greenkeeper branches + PRs build on every branches
+# Avoid double build on PRs (See https://github.com/travis-ci/travis-ci/issues/1147)
 branches:
   only:
     - master
     - /^greenkeeper.*$/
+
+# Retrieve 999 commits (default is 50) so semantic-release can analyze all commits when there is more than 50 on a PR
 git:
   depth: 999
+
+# Retry install on fail to avoid failing a build on network/disk/external errors
 install:
   - travis_retry npm install
+
 script:
   - npm run test
+
 after_success:
   - if [ -n "${CODECOV_TOKEN:-}" ]; then npm run codecov; fi
   - npm run coverage