build(travis): add switch of npm install script

Author: michaelwittwer

.travis.yml

@@ -16,10 +16,10 @@ node_js:
 # of updating the package lock.
 install:
 #  decide if running on greenkeeper branch or not
-#- case $TRAVIS_BRANCH in greenkeeper*) npm i;; *) npm ci;; esac;
+- case $TRAVIS_BRANCH in greenkeeper*) npm i;; *) npm ci;; esac;
 # somehow the above command fails when we have a cache available on travis - needs some more investigation, stick with
 # npm i for now
-- npm ci
+#- npm ci
 
 notifications:
   email: false