Update travis.yml to remove greenkeeper specific parts. Use npm ci instead of install and update.

.travis.yml

@@ -108,16 +108,9 @@ addons:
       - ubuntu-toolchain-r-test
     packages:
       - g++-4.8
-before_install:
-# package-lock.json was introduced in npm@5
-- '[[ $(node -v) =~ ^v9.*$ ]] || npm install -g npm@latest' # skipped when using node 9
-- npm install -g greenkeeper-lockfile
 install:
   - sudo -H pip install -r requirements.txt
-  - npm --production=false install
-  - npm --production=false --legacy-peer-deps update
-before_script: greenkeeper-lockfile-update
-after_script: greenkeeper-lockfile-upload
+  - npm ci
 jobs:
   include:
   - stage: test