build: fix paths for examples tests

scripts/ci/build.sh

@@ -37,7 +37,7 @@ travisFoldEnd "tsc a bunch of useless stuff"
 
 
 # Build integration tests
-if [[ ${CI_MODE} == "e2e" ]]; then
+if [[ ${CI_MODE:-} == "e2e" ]]; then
   travisFoldStart "build.integration"
     cd "`dirname $0`/../../integration"
     ./build_rxjs_es6.sh
@@ -47,7 +47,7 @@ fi
 
 
 # Build angular.io
-if [[ ${CI_MODE} == "aio" ]]; then
+if [[ ${CI_MODE:-} == "aio" ]]; then
   travisFoldStart "build.aio"
     cd "`dirname $0`/../../aio"
     yarn run build