ci: add comment and remove debugging printenv statement

.travis.yml

@@ -55,6 +55,7 @@ matrix:
     - env: "CI_MODE=browserstack_optional"
 
 before_install:
+  # source the env.sh script so that the exported variables are available to other scripts later on
   - source ./scripts/ci/env.sh print
 
 install:

scripts/ci/install.sh

@@ -50,7 +50,6 @@ if [[ ${TRAVIS} && (${CI_MODE} == "aio" || ${CI_MODE} == "docs_test") ]]; then
   # angular.io: Install all yarn dependencies according to angular.io/yarn.lock
   travisFoldStart "yarn-install.aio"
     (
-      printenv
       cd ${PROJECT_ROOT}/aio
       yarn install
     )